Seismic Assessment of 91 Willow Street Campus Buildings

Transcription

1 Report Seismic Assessment of 91 Willow Street Campus Buildings Prepared for Tauranga City Council Prepared by Beca Ltd (Beca) 10 April 2015

2 Seismic Assessment of 91 Willow Street Campus Buildings Revision History Revision Nº Prepared By Description Date A Craig Lavin Draft Report 10/04/2015 Document Acceptance Action Name Signed Date Prepared by Reviewed by Approved by on behalf of Craig Lavin Rob Jury Krish Shekaran Beca Ltd Beca 2015 (unless Beca has expressly agreed otherwise with the Client in writing). This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk. Beca // 10 April // NZ // i

3 Seismic Assessment of 91 Willow Street Campus Buildings Contents 1 Scope of Services 1 2 Investigations and Findings 2 3 Conclusions and Next Steps 7 Appendices Appendix A Library Building Confirmation of Strengthening Appendix B Seismic Assessment Willow Street Campus Building A & C Appendix C Plan of Opus Test Locations Appendix D Overall Site Plan Beca // 10 April // NZ // i

4 1 Scope of Services Beca s scope of work is as below: a. Geotechnical interpretation of CPT data provided by TCC to assess the soils class and the likely effects of liquefaction on all buildings in a 1 in 500 year seismic event [IL2]. Provide inputs to mitigate these effects in the costing of remedial conceptual designs referred below. b. Independent seismic assessment for Blocks A and C as per the scope below: i. Review structural drawings provided by TCC. ii. Visit the site and assess if the building structure is generally as per the drawings. iii. Carry out engineering calculations to estimate the seismic capacity of the existing building, the building drawings and any other available information. The detailed assessment will be carried out in accordance with the recommendations of the New Zealand Society for Earthquake Engineering guidelines for assessing existing buildings. The assessment will consider the effect for any liquefaction expected at a 1 in 500 year seismic event on the structural system. iv. Assess whether the building is an earthquake-prone building, [ie achieves less than 34% of the required strength of a new building (<34%NBS)]. v. Assess whether the building is an earthquake risk (ie achieves less than 67%NBS). vi. Comment on the performance of the stairs and any recommended remediation. vii. Report on assessment findings and (if required) remedial concepts to strengthen these buildings to 67%NBS at IL2 (including stairs), estimated construction timeframes and construction cost estimates to an accuracy of -+15%. The report will include a commentary on construction methodology of any remedial measures required. c. Carry out following scope on Block B: i. Review structural calculations alterations completed in 2006 for Block B and assess the %NBS. The assessment will consider the effect of any liquefaction expected at a 1 in 500 year seismic event on the structural system. ii. Review structural drawings provided by TCC. iii. Visit the site and assess if the building structure is generally as per the drawings and whether the previously recommended remediation works have been carried out. iv. Report on assessment findings and (if required) provide remedial concepts to strengthen these buildings to 67%NBS at IL2 (including stairs), estimated construction timeframes and construction cost estimates to an accuracy of -+15%. We will include commentary on methodology. The report will include commentary on construction methodology of any remedial measures if required. d. Carry out the following scope for the administration building: Beca // 10 April // NZ // page 1

5 i. Provide confirmation of the current %NBS of the Administration building at 91 Willow Street following the plant room strengthening works carried out in ii. Revise the concept for strengthening the Administration building to 67%NBS at Importance Level 2 accounting for the effects of any liquefaction expected in a 1 in 500 year seismic event. iii. Provide construction cost estimates to an accuracy of +-15%. These costs will be presented as a standalone exercise and if the building was stripped down to the bare structure to remedy the weather tightness issues. The report will include a commentary on the construction methodology and estimated construction timeframes. iv. Comment on the performance of the stairs and any recommended remediation. 2 Investigations and Findings Geotechnical Summary We consider that there is insufficient evidence to demonstrate that the site subsoil class is Class C. Whilst it is possible that the site subsoil class maybe Class C, in the absence of conclusive evidence, we have completed our assessment considering site subsoil class D. Liquefaction is indicated from a depth of 2.5m below ground level. If liquefaction were to occur during a seismic event, the potential exists for a loss of bearing support to the pad foundations of the Block A and C buildings. This has been considered in our structural assessment of the buildings. We consider that there is a low risk of lateral spreading towards the harbour occurring at 67% of Peak Ground Acceleration (PGA) defined for the ULS event in NZS Site Subsoil Class We have based our interpretation on the recent Cone Penetration Tests (CPTs) undertaken for TCC by Opus International Consultants Limited 1. The relevant CPTs are CPT02, CPT03 and CPT04. CPT02 refused (i.e. could not be advanced further) at around 20m below ground level, whilst CPT03 and CPT04 were terminated in dense materials at their target depths of 22m and 20m below ground level respectively. For the site subsoil class to be Class C in terms of NZS1170.5: requires the site period of the soils above the underlying bedrock to be less than 0.6 seconds. The site period is determined as a function of the shear wave velocity and the depth to bedrock (defined as rock with an Unconfined Compressive Strength UCS of more than 1MPa). Shear wave velocity measurements are available from CPT04 however the depth to bedrock is not known. 1 Opus International Consultants Limited (2014). Tauranga City Council Civic Campus Structural Review Wharf Street and Willow Street Tauranga CBD. Prepared for Tauranga City Council. 2 NZS : New Zealand Standard: Structural Design Actions, Part 5 Earthquake Actions, New Zealand Beca // 10 April // NZ // page 2

6 CPT02 refused at a depth of 20m below ground level. Whilst CPT refusal might indicate that bedrock was encountered, encountering a bedrock material at such a depth would be unusual given the geology of Tauranga. We therefore consider that there is insufficient evidence to demonstrate that the site subsoil class is Class C. Whilst it is possible that the site subsoil class maybe Class C, in the absence of conclusive evidence, we recommend that the site subsoil class should be taken as D. If the site subsoil class is found to be critical to the outcome of the detailed seismic assessment, then we recommend that a deep borehole (i.e. 60m+) with downhole seismic shear wave velocity testing be undertaken. Liquefaction Assessment We have carried out a very preliminary liquefaction assessment using the data from CPT02, CPT03 and CPT04, based on the following criteria: Importance Level 2, Ultimate Limit State (ULS) Earthquake = 1/500 year Design event = 67% of Peak Ground Acceleration (PGA) defined for the ULS in NZS Groundwater level assumed at 2.5m below ground level For completeness, we have considered the site class as both Class C or D. Our assessments have been carried out in accordance with the New Zealand Geotechnical Society liquefaction guideline 3, using PGA s derived from NZS1170.5:2004, with a weighted magnitude of 7.5. The results of the analyses are presented in Table 1 below. Table 1 - Liquefaction Summary Case PGA Magnitude Liquefaction Settlement (mm) Class C 0.18g Class D 0.15g Based on the analyses and results above we can make the following observations: The soils are not uniform across the site. For example the soils encountered in CPT03 are typically more cohesive than those encountered in the other two CPTs. The soils encountered in CPT04 are the most granular and most liquefiable. Hence CPT04 exhibits the most liquefaction settlements. The difference between the liquefaction potential indicated under Class C and D conditions is relatively small. Liquefaction immediately below the water table is indicated in 2 out of the 3 CPTs, i.e. at 2.5m depth. Based on the settlement estimates above, we would expect differential liquefaction settlements across the building footprint in the order of 100 to 150mm for the 67% design event defined above. Liquefaction in an event 33% of that defined for the ULS in NZS (PGA = g) is likely to be very limited, if it occurs at all. 3 New Zealand Geotechnical Society (2010). Geotechnical Earthquake Engineering Practice, Module 1- Guideline for the identification, assessment and mitigation of liquefaction hazards. Beca // 10 April // NZ // page 3

7 By inspection, the ground effects in a 1 in 500 year return period event will be worse than that for the 67% design event defined above. The PGAs and Magnitude used in the analyses are likely to be upper bound values. It s possible that a Site Specific Hazard Assessment could determine that the hazard is less than that suggested by NZS1170. Comparison to a corresponding PGA and representative Magnitude derived from the NZTA Bridge Manual (3 rd edition) 4 suggests that lower liquefaction potential is possible. Lateral Spreading Although liquefaction is indicated in the 67% design event case considered, the variable nature of the soils identified suggests that liquefaction would likely be experienced in discontinuous zones, rather than as a uniform layer extending to the harbour to the west. We therefore consider that there is a low risk of lateral spreading towards the harbour occurring under the 67% design event case. Bearing Capacity Liquefaction is indicated from a depth of 2.5m below ground level. We understand that the buildings foundations are typically founded at a depth of around 1.0 to 1.5m below ground level. If liquefaction were to occur during a seismic event, then the potential exists for larger strains to be experienced under some foundations as a result of a loss of bearing support from the liquefied soils. The Administration building foundations are strip footings founded at around 1.5m below ground level. We note that the basement level around the stair lift shaft lies at around 2.5m below ground level, so could be directly bearing onto potentially liquefiable soils. This zone is the most likely to experience a loss of bearing support. By contrast buildings A and C are founded on pad foundations founded at around 1.5m below ground level. The consequence of a loss of bearing support under some foundations has been considered in the structural seismic assessments, see below. Blocks A & C Offices and Customer Services Introduction We have carried out a detailed seismic assessment of building Blocks A and C. Details on this assessment are provided in our report titled Seismic Assessment Willow Street Campus Buildings A and C, dated 20 March Below is a summary from this report. The original lower two storeys of Block A and C consist of reinforced concrete framed structures with Unislab concrete flooring, constructed circa The roofs were originally used as a car park prior to the construction of a steel framed second storey on both buildings circa The primary lateral load resisting system of the original structures is reinforced concrete moment frames on shallow concrete foundations. The lateral loads in the top floor additions are resisted by plywood and plasterboard lined timber walls and steel portals. Roof bracing consists of a plywood roof diaphragm in Block A and steel roof bracing in Block C. 4 New Zealand Transport Agency Bridge Manual 3rd Edition, SP/M/022, May Beca // 10 April // NZ // page 4

8 There are concrete slab pedestrian bridges at the first and second floor levels spanning between Blocks A, B, C, and Admin building. The atrium areas between Block A, B and C buildings is covered at roof level with a mixed glazing/cladding system. Assessed Structural Performance We are concerned that the glazing in the atrium areas between the buildings, particularly at roof level, may be vulnerable to relative movement between the buildings during seismic shaking. If there is not suitable movement tolerance in this system, there may be a risk of shattered glass or glazing panels falling into the public access space below. We are in the process of engaging a façade specialist to inspect the atrium glazing and report on the movement capability of the glazing system and the associated seismic performance. The outcome of this further assessment work may affect the building seismic scores provided below. The results of our quantitative assessment of the structure for building Block A indicate the building achieves approximately 55%NBS in terms of the performance for life safety as determined using the New Zealand Society of Earthquake Engineering (NZSEE) guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade C building following the definition of the NZSEE building grading scheme. Grade C buildings have approximately 5-10 times the seismic risk compared to a new building, indicating a medium risk exposure. This seismic score for this building is limited by a shortfall in the lateral capacity of the braced timber walls in the upper storey extension, for shaking in the east-west direction. Building Block C achieves greater than 67%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade B building or better following the definition of the NZSEE building grading scheme. Grade B buildings have approximately 2-5 times the seismic risk relative to a new building, indicating a low or medium risk exposure. We have assessed the expected performance of the stairs and link bridges based on the available details and considering estimated building movements. We believe these can perform satisfactorily for the drifts we have calculated when the buildings area subject to 67% loading defined for the ULS event in NZS Consideration of Liquefaction We have assessed the effect on the structure of losing bearing support under a pad foundation resulting from a potential liquefaction case, for the 67% ULS design event being considered. Our assessment shows that although there could be significant damage to the building in this event, as also concluded by Opus, the building is capable of maintaining structural integrity sufficient to achieve life-safety objectives as defined by the NZSEE guidelines. Seismic Retrofit We propose replacement of the wall linings for five walls on level 2 of Block A. This would consist of removal of existing plasterboard linings, installation of standard Gib system hold down fixings to studs and installation of plywood and plasterboard linings as required for the Gib BR7 system. This strengthening would lift the seismic score for Block A building to above 67%NBS. Block B Library Block Beca carried out a limited assessment of the primary means of the earthquake resistance of the Block B Library Block (including the seismic mass of the upper level extension added in 2007) and found that the building is likely to perform satisfactorily in a code level earthquake provided that the strengthening originally recommended by Connell Mott MacDonald in 2006 was carried out.. Beca // 10 April // NZ // page 5

9 We reviewed the construction records and could not confirm that the strengthening works were completed. So we carried out a visual inspection and found that the remedial strengthening was completed and this was further confirmed by the contractor Conspec construction (refer attached as Appendix C). On this basis, we are satisfied that this strengthening work has been completed. No further work is required. We revisited the seismic assessment to understand the effect of the expected settlements in the event of liquefaction. The foundation system for this building is similar to the Building A and C and so we expect similar performance as for Building A and C. Refer Consideration of Liquefaction, above. Based on our findings, we assess the Block B- Library Building to achieve 67%+NBS in terms of life safety performance in a 1 in 500 year (Importance Level 2) seismic event. Please note that a 67%NBS building is at 5 times the risk of collapse compared to a new 100%NBS building. We note that the outcome of further glazing assessment work, yet to be undertaken, may affect this score. We noted potentially non-ductile columns and these will sustain some damage in a 67% ULS event, while not preventing the building from sustaining 67%NBS, NZSEE. Columns identified as non-ductile exhibit detailing features which have the potential to result in brittle behaviour during seismic shaking. This means that beyond a certain level of lateral movement, the columns cannot be relied upon to provide gravity support for the structure. We also reviewed the stair construction. The stairs are connected to SHS posts at mid-landing. Although we expect some damage around the SHS posts connections to the floor at a 67%NBS, we expect them to perform satisfactorily. Administration Block Beca had carried out a seismic assessment on the Administration Block in The building was assessed as earthquake prone and immediate remedial strengthening to the plant room structure was recommended. These works have been completed and the current %NBS of the building is 40%NBS (Grade C building). A building with less than 34%NBS is categorised as an Earthquake Prone Building (EPB) and a building with less than 67%NBS is categorised as an Earthquake Risk Building (ERB). The Administration Block is therefore categorised as an Earthquake Risk Building. We had provided concepts to strengthen the building to 67%NBS and 100%NBS. We revisited the seismic assessment to understand the effect of the expected settlements in the event of liquefaction and our findings are as below: a. The foundations system consists of strip foundations - 1.6m wide in both directions with a 1.0m deep wall connecting the strip foundation to the floor slab. b. There is approximately 1.0m of soil crust between the u/s of the foundations and the layer of the soil expected to liquefy. We expect the foundation raft described above and the soil crust combined with the structural system of the building to be able to withstand the expected settlement due to liquefaction without causing collapse. However we do expect some damage. Based on our findings above the concept proposed to strengthen the building to 67%NBS in our previous assessment remains unchanged. This option consists of new shear walls, some strengthening to columns and new foundations. No work is required to the stairs. Beca // 10 April // NZ // page 6

10 3 Conclusions and Next Steps Geotechnical Site Subsoil Class We have reviewed the 2014 Opus CPT data provided. We consider that there is insufficient evidence at this stage to demonstrate that the site subsoil class is Class C. We recommend that the site subsoil class should be taken as D. Liquefaction Liquefaction is expected to occur in an earthquake with shaking equivalent to 67% of that defined for the ULS in NZS1170.5, with liquefaction indicated from a depth of 2.5m below ground level. Between 150mm and 300mm of liquefaction settlement are indicated, for the above case. Liquefaction differential settlements in order of 100mm to 150mm are possible across the building footprints, for the above case. Liquefaction in an event 33% of that defined for the ULS in NZS (PGA = g) is likely to be very limited, if it occurs at all. We consider that there is a low risk of lateral spreading occurring towards the harbour for the 67% case noted above. Bearing Capacity The buildings foundations are typically founded at a depth of around 1.0m to 1.5m below ground level. If liquefaction were to occur during a seismic event, the potential exists for larger strains to be experienced under some foundations as a result of a loss of bearing support from the liquefied soils. The consequence of a loss of bearing support under some foundations has been considered in the structural seismic assessments. Blocks A & C - Offices and Customer Services Our assessment of the structure for building Block A indicates the building achieves approximately 55%NBS, a Grade C building, in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170. The building seismic score is limited by a shortfall in the lateral capacity of the braced timber walls in the upper storey extension, for shaking in the east-west direction. Building Block C achieves greater than 67%NBS, and is therefore a Grade B building or better. We propose seismic retrofit work consisting of replacement of the wall linings for five walls on level 2 of Block A. This would lift the seismic score for Block A building to above 67%NBS. Block B We assessed the Block B - Library Building (accounting for the expected liquefaction settlements) to achieve 67%+NBS (Grade B) in terms of life safety performance in a 1 in 500 year (Importance Level 2) seismic event. A building with less than 34%NBS is categorised as an Earthquake Prone Building (EPB) and a building with less than 67%NBS is categorised as an Earthquake Risk Building (ERB). Block B is there considered not to be an earthquake-risk or earthquake-prone building and is a Grade B building. Beca // 10 April // NZ // page 7

11 We can provide options to strengthen the building to a Grade A (>80%NBS). We recommend that the non-structural elements such as services/plant be assessed and upgraded. Atrium Glazing Beca do not have suitable expertise to assess glazing systems. At the request of TCC, we are in the process of engaging a glazing façade specialist to inspect the atrium glazing and report on the movement capability of the glazing system and the associated seismic performance. The outcome of this further assessment work may affect the building seismic scores provided above. Administration Block We assess the Administration Building (accounting for the expected liquefaction settlements) to achieve 40%+NBS in terms of life safety performance in a 1 in 500 year (Importance Level 2) seismic event. A building with less than 34%NBS is categorised as an Earthquake Prone Building (EPB) and a building with less than 67%NBS is categorised as an Earthquake Risk Building (ERB). The Administration Block B is there considered as an earthquake-risk building and is a Grade C building. We recommend strengthening to 67%NBS in conjunction with the repair works intended to be carried out to fix the water tightness issues. We also recommend that the non-structural elements such as services/plant be assessed and upgraded, if required. Refer Appendix D overall site plan showing current scores and scope of work for each building. Beca // 10 April // NZ // page 8

12 Appendix A Library Building Confirmation of Strengthening Beca // 10 April // NZ // page 9

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16 Appendix B Seismic Assessment Willow Street Campus Building A & C Beca // 10 April // NZ // page 10

17 Report Seismic Assessment - Willow Street Campus - Building A & C Prepared for Tauranga City Council Prepared by Beca Ltd (Beca) 20 March 2015

18 Revision History Revision Nº Prepared By Description Date A Craig Lavin DRAFT For Review 20/03/2015 Document Acceptance Action Name Signed Date Prepared by Reviewed by Approved by on behalf of Craig Lavin Rob Jury Krish Shekaran Beca Ltd Beca 2015 (unless Beca has expressly agreed otherwise with the Client in writing). This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk // NZ // i

19 Executive Summary Background This seismic assessment report has been prepared for Tauranga City Council (TCC) to describe the results of our quantitative assessment of Blocks A and C buildings at 91 Willow Street, Tauranga. TCC are the owners of these buildings. This follows detailed seismic assessments carried out by OPUS for Blocks A, B and C dated May This report has been prepared in accordance with the scope of work described in the proposal dated 16 February Description of Buildings The TCC campus at 91 Willow Street consists of three buildings of similar design (Blocks A, B and C) designed and constructed circa The buildings were likely to have been designed to the loadings standard NZS4203:1984 and concrete standard NZS3101:1982. The primary use of Blocks A and C is office space with some retail areas on the ground floor. The original lower two storeys of Block A and C consist of reinforced concrete framed structures with Unislab concrete flooring. The roofs were originally used as a car park prior to the construction of a steel framed second storey on both buildings circa The primary lateral load resisting system of the original structures is reinforced concrete moment frames on shallow concrete foundations. The lateral loads in the top floor additions are resisted by plywood and plasterboard lined timber walls and steel portals. Roof bracing consists of a plywood roof diaphragm in Block A and steel roof bracing in Block C. There are concrete slab pedestrian bridges at the first and second floor levels spanning between Blocks A, B, C, and Admin buildings. There are plant platforms on the roof of both Blocks A and C. Geotechnical Considerations We consider that there is insufficient evidence to demonstrate that the site subsoil class is Class C. Whilst it is possible that the site subsoil class maybe Class C, in the absence of conclusive evidence, we have completed our assessment considering site subsoil class D. Liquefaction is indicated from a depth of 2.5m below ground level. If liquefaction were to occur during a seismic event, the potential exists for a loss of bearing support to the pad foundations of the Block A and C buildings. This has been considered in our structural assessment of the buildings. We consider that there is a low risk of lateral spreading towards the harbour occurring at 67% of Peak Ground Acceleration (PGA) defined for the ULS event in NZS Assessed Structural Performance We are concerned that the glazing in the atrium areas between the buildings, particularly at roof level, may be vulnerable to relative movement between the buildings during seismic shaking. If there is not suitable movement tolerance in this system, there may be a risk of shattered glass or glazing panels falling into the public access space below. Beca do not have suitable expertise to assess glazing systems. At the request of TCC, we are in the process of engaging a glazing façade specialist to inspect the atrium glazing and report on the movement capability // NZ // ii

20 of the glazing system and the associated seismic performance. The outcome of this further assessment work may affect the building seismic scores provided below. The results of our quantitative assessment of the structure for building Block A indicate the building achieves approximately 55%NBS in terms of the performance for life safety as determined using the New Zealand Society of Earthquake Engineering (NZSEE) guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade C building following the definition of the NZSEE building grading scheme. Grade C buildings have approximately 5-10 times the seismic risk compared to a new building, indicating a medium risk exposure. The results of our quantitative assessment of the structure for building Block C indicate the building achieves greater than 67%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade B building or better following the definition of the NZSEE building grading scheme. Grade B buildings have approximately 2-5 times the seismic risk relative to a new building, indicating a low or medium risk exposure. A building achieving less than 34%NBS is categorised as an Earthquake Prone Building (EPB) and a building achieving less than 67%NBS is categorised as an Earthquake Risk Building (ERB). Block A and C are therefore not categorised as Earthquake Prone buildings. Block A is categorised as an Earthquake Risk building. Our assessment identified the following structural weaknesses which govern the seismic performance: A shortfall in the lateral capacity of the timber wall bracing for the upper storey extension to Block A limits the seismic building score to less than 67%NBS for shaking in the east-west direction. In addition to our findings in respect of the overall building behaviour noted above, the expected performance of the site and selected secondary structural elements have also been assessed: Glazing: Potential risk to public from atrium glazing, as discussed above. Liquefaction: Our assessment shows that although there could be significant damage to the building in this event, the building is capable of maintaining structural integrity sufficient to achieve life safety objectives as defined by the NZSEE guidelines. Stairs: We have assessed the expected performance of the stairs considering estimated building movements as defined by MBIE Practice Advisory 13. We believe the stairs are likely to remain available for egress for building drifts up to the level required by the advisory. Link bridges: We have assessed the expected performance of the link bridges based on the available details and considering estimated building movements. We believe these can perform satisfactorily for the drifts we have calculated when the buildings area subject to 67% loading defined for the ULS event in NZS Seismic Retrofit Options The following seismic retrofit concept is to address the identified weakness in the lateral capacity of the timber wall bracing for upper storey extension to Block A. This concept has been developed for discussion with TCC. We propose replacement of the wall linings for five walls on level 2 of Block A. This would consist of removal of existing plasterboard linings, installation of standard Gib system hold down fixings to studs and installation of plywood and plasterboard linings as required for the Gib BR7 system. This strengthening would lift the seismic score for Block A building to above 67%NBS // NZ // iii

21 Next Steps In order to assess the seismic risk and performance of the atrium glazing, a specialist façade engineer is required. Beca do not have suitable expertise in this area so a specialist façade engineer is being engaged to carry out an assessment and report on this risk. This work is not complete at the time of writing. We recommend that TCC consider carrying out the following next steps: Carry out strengthening of the timber walls at level 2 of Block A in order to lift the building seismic score above the 67%NBS threshold identified by TCC. Further recommendations may be provided following completion of the glazing assessment work // NZ // iv

22 Contents 1 Introduction Scope of Assessment Regulatory Environment and Design Standards Assessment Methodology Explanatory Statement 3 2 Building Description Building A & C Site Conditions Structural System 8 3 Results of Seismic Assessment 10 4 Commentary on Associated Seismic Risks Stairs Link Bridges Liquefaction Risks from Non-structural Building Elements 12 5 Assessment of Seismic Risk Seismic Risk and Performance Levels 13 6 Seismic Retrofit and Strengthening Retrofit and Strengthening Options Preliminary Cost Estimate 1 7 Next Steps 1 Appendices Appendix A Sources of Information Appendix B Seismic Assessment Assumptions Appendix C Building Inspection Photographs Appendix D Structural Drawings // NZ // i

23 1 Introduction This seismic assessment report has been prepared for Tauranga City Council (TCC) to describe the results of our quantitative assessment of Blocks A and C buildings at 91 Willow Street, Tauranga. TCC are the owners of these buildings. This follows detailed seismic assessments carried out by OPUS for Blocks A, B and C dated May This report has been prepared in accordance with the scope of work described in the proposal dated 16 February Scope of Assessment The purpose of this assessment is to establish the seismic risk and vulnerability of Blocks A and C and, if necessary, to propose concepts for structural remediation to achieve a level of seismic risk acceptable to Tauranga City Council. Our scope of work includes: Review of available structural and architectural drawings provided by TCC. Visit the site and assess if the building structure is generally as per the drawings. Carry out engineering calculations, including the assembly of an analytical model, to estimate the seismic capacity of the existing building. The detailed assessment will be carried out in accordance with the recommendations of the New Zealand Society for Earthquake Engineering guidelines for assessing existing buildings. The effect for any liquefaction expected at a 1 in 500 year seismic event on the structural system will be accounted for in the assessment. Assess whether the building is an earthquake-prone building, [i.e. achieves less than 34% of the required capacity of a new building (<34%NBS). Assess whether the building is an earthquake risk (i.e. achieves less than 67%NBS). Comment on the performance of the stairs and any recommended remediation. Report on assessment findings and, if required, remedial concepts to strengthen these buildings to 67%NBS at IL2 (including stairs), estimated construction timeframes and construction cost estimates to an accuracy of -+15%. We will include a commentary on construction methodology. 1.2 Regulatory Environment and Design Standards Earthquake-Prone Buildings (EPBs) are defined in Section 122 of the Building Act 2004 as buildings whose ultimate capacity will be exceeded in a moderate earthquake and would likely result in injury or death or damage to any other property. A moderate earthquake is defined as approximately one-third as strong as the earthquake shaking assumed in the design of a new building. Using the 2006 NZSEE Guidelines terminology, a building that achieves less than 34% of the New Building Standard (%NBS) is categorised as Earthquake-Prone. The NZSEE Guidelines also define a building achieving less than 67%NBS, as Earthquake-Risk. The NZSEE Guidelines recommend a minimum target strengthening level of 67%NBS. The Royal Commission into the Canterbury Earthquakes has recently recommended changes in respect of EPBs including recommendations to change the allowable time to assess whether buildings are earthquake prone (2 years for URM buildings and 5 years for other buildings) and then strengthen buildings to above 34%NBS (a total timeframe of 7 years for URM buildings and 15 years for other buildings). The government, under the Ministry of Business, Innovation and Employment (MBIE) has considered these recommendations and has proposed legislative changes. The proposed legislative changes have recently been introduced with a time frame of 5 years for assessment, whether or not buildings are earthquake prone, // NZ // page 1

24 and a total of 15 years to strengthen all buildings to above 34%. These timeframes and strengthening levels are proposed to apply nationally. No change to the definition of an earthquake prone building has been proposed at this stage. It is considered impractical and unaffordable to design every building to withstand the largest earthquake imaginable. Consequently, with respect to the determination of design loads for natural hazards, the New Zealand Loading Standard adopts a probabilistic approach that takes into account the exposure hazard at a given location, along with factors such as building importance. Thus, the Loading Standard may be said to adopt a risk management approach in setting the loading levels that a given building is required to withstand. For normal use buildings (e.g. offices, apartments), the design earthquake load is set at the 1 in 500 year return period earthquake event. This event has approximately a 10% probability of exceedence over the assumed 50 year life of a building. 1.3 Assessment Methodology We have adopted a stepped analysis approach to undertaking the seismic assessment of Blocks A and C starting with simpler analysis methods and progressively employing more sophisticated methods of analysis and calculations in order to determine the seismic vulnerability of the building. The techniques used are generally as outlined in the June 2006 report by the New Zealand Society for Earthquake Engineering entitled Assessment and Improvement of the Structural Performance of Buildings in Earthquakes (2006 NZSEE Guidelines). Our methodology is briefly summarized below: Review of the available structural and architectural drawings and any calculations available to us (provided by TCC) to identify the main structural elements and any apparent structural weaknesses that may significantly reduce the seismic performance of the building. The critical structural weakness is the structural weakness determined to have the lowest score. Visual inspection of key elements of the building including the pedestrian bridges spanning between Blocks A, C, Block B and Admin building; the columns and beams of the reinforced concrete levels of the buildings; and the low level walls between the columns in the South West corner of Block A. Calculation of the expected seismic loads on the building following the current New Zealand loading standards (NZS1170). Hand analysis of selected critical elements of the building to determine the likely failure mechanisms of these subassemblies, and the whole building. Development of an elastic three-dimensional (3D) ETABS computer model of Block A building for analysis of the force distributions and critical structural elements using the NZ loading code response spectrum. Block A and C buildings are considered vertically irregular due to the variation in weight and lateral stiffness between the lower concrete structure and steel upper structure. The resulting amplification on seismic accelerations for the upper storeys have been considered in our assessment. Development of a Spacegass model of the stair assembly and an analysis of the assembly based on the drifts obtained from the building analysis to review expected performance of the stairs under seismic loading. Review of link bridge performance based on drifts obtained from the building analysis and detailing from council archive drawings. Determination of the likely seismic performance of the building compared with an equivalent new building at the site based on our inspections, the structural weaknesses identified, our calculations, and our engineering judgment // NZ // page 2

25 1.4 Explanatory Statement This report has been prepared by Beca at the request of our Client and is exclusively for our Client s use for the purpose for which it is intended in accordance with the agreed scope of work. Beca accepts no responsibility or liability to any third party for any loss or damage whatsoever arising out of the use of or reliance on this report by that party or any party other than our Client. The inspections of the building discussed in this report have been undertaken to assist in the structural assessment of the building structure for seismic loads only. This assessment does not consider gravity or wind loading or cover building services or fire safety systems, or the building finishes, glazing system (other than where specifically identified in this report) or the weather tightness envelope. This assessment does not include an assessment of the building condition or repairs that may be required. No geotechnical site investigations have been undertaken by Beca. Beca is not able to give any warranty or guarantee that all possible damage, defects, conditions or qualities have been identified. The work done by Beca and the advice given is therefore on a reasonable endeavours basis. Except to the extent that Beca expressly indicates in the report, no assessment has been made to determine whether or not the building complies with the building codes or other relevant codes, standards, guidelines, legislation, plans, etc. The assessment is based on the information available to Beca at the time of the assessment and assumes the construction drawings supplied are an accurate record of the building. Further information may affect the results and conclusion of this assessment. The information used to undertake the seismic assessment is listed in Appendix A. Beca has not considered any environmental matters and accepts no liability, whether in contract, tort, or otherwise for any environmental issues. The basis of Beca s advice and our responsibility to our Client is set out above and in the terms of engagement with our Client // NZ // page 3

26 2 Building Description 2.1 Building A & C Summary information about the building is presented in the following table. Reference Information used to undertake this seismic assessment is listed in Appendix A. Building Summary Information Item Details Comment Building name TCC Civic Building Block A & C Street Address 91 Willow St, Tauranga Age 1987 Additional storey designed 2003 Description / Building Occupancy Ground Floor office and retail space 1st Floor office space 2nd Floor office space Roof plant platforms Building Footprint / Floor Area Block A 535m 2 No. of storeys / basements Structural system Earthquake resisting system Foundation system Stair system Other notable features Past seismic strengthening Construction information Block C 370m 2 Three-storey building. No basement Reinforced concrete framed structure with reinforced concrete floor slab-ongrade and first floor. Second storey (top floor) steel framed structure with timber framed walls. Reinforced concrete frames in both directions for original first two storeys. Braced timber framed walls in both directions in top floor. With plywood roof diaphragm in Block A and steel roof bracing in Block C. Shallow foundation pads and strip footing with tie beams. Precast concrete support on steel beams and posts Concrete slab pedestrian bridges at the first and second floor levels spanning between Blocks A, C, B and Admin building. Not aware of any strengthening Available original structural and architectural drawings provided by TCC Transverse (east-west) and Longitudinal (north-south) building lengths measuring 24m and 22m respectively for Block A and 24m and 15m for Block C. False concrete columns each side of core columns add significant stiffness to the frames and reduced the available hinge region and curvature ductility. It appears that the structural drawing set is incomplete, or further drawings were developed that have not been stored by TCC // NZ // page 4

27 Item Details Comment Likely Design Standards NZS4203:1984 NZS3101:1982 NZS1170:2002 NZS3404:1997 For design of additional storey Figure 1 Aerial Photograph of the TCC Campus (source: Google Earth) // NZ // page 5

28 Figure 2 Street view of Block A and C Buildings (source: Google Earth) Additional photographs of the building are included in Appendix C. 2.2 Site Conditions Site Subsoil Class We have based our interpretation on the recent Cone Penetration Tests (CPTs) undertaken for TCC by Opus International Consultants Limited 1. The relevant CPTs are CPT02, CPT03 and CPT04. CPT02 refused (i.e. could not be advanced further) at around 20m below ground level, whilst CPT03 and CPT04 were terminated in dense materials at their target depths of 22m and 20m below ground level respectively. For the site subsoil class to be Class C in terms of NZS1170.5: requires the site period of the soils above the underlying bedrock to be less than 0.6 seconds. The site period is determined as a function of the shear wave velocity and the depth to bedrock (defined as rock with an Unconfined Compressive Strength UCS of more than 1MPa). Shear wave velocity measurements are available from CPT04 however the depth to bedrock is not known. CPT02 refused at a depth of 20m below ground level. Whilst CPT refusal might indicate that bedrock was encountered, encountering a bedrock material at such a depth would be unusual given the geology of Tauranga. We therefore consider that there is insufficient evidence to demonstrate that the site subsoil class is Class C. Whilst it is possible that the site subsoil class maybe Class C, in the absence of conclusive evidence, we recommend that the site subsoil class should be taken as D. 1 Opus International Consultants Limited (2014). Tauranga City Council Civic Campus Structural Review Wharf Street and Willow Street Tauranga CBD. Prepared for Tauranga City Council. 2 NZS : New Zealand Standard: Structural Design Actions, Part 5 Earthquake Actions, New Zealand // NZ // page 6

29 If the site subsoil class is found to be critical to the outcome of the detailed seismic assessment, then we recommend that a deep borehole (i.e. 60m+) with downhole seismic shear wave velocity testing be undertaken Liquefaction Assessment We have carried out a very preliminary liquefaction assessment using the data from CPT02, CPT03 and CPT04, based on the following criteria: Importance Level 2, Ultimate Limit State (ULS) Earthquake = 1/500 year Design event = 67% of Peak Ground Acceleration (PGA) defined for the ULS in NZS Groundwater level assumed at 2.5m below ground level For completeness, we have considered the site class as both Class C or D. Our assessments have been carried out in accordance with the New Zealand Geotechnical Society liquefaction guideline 3, using PGA s derived from NZS1170.5:2004, with a weighted magnitude of 7.5. The results of the analyses are presented in Table 1 below. Table 1: Liquefaction Summary Case PGA Earthquake (M L ) Liquefaction Settlement (mm) Class C 0.18g Class D 0.15g Based on the analyses and results above we can make the following observations: The soils are not uniform across the site. For example the soils encountered in CPT03 are typically more cohesive than those encountered in the other two CPTs. The soils encountered in CPT04 are the most granular and most liquefiable. Hence CPT04 exhibits the most liquefaction settlements. The difference between the liquefaction potential indicated under Class C and D conditions is relatively small. Liquefaction immediately below the water table is indicated in 2 out of the 3 CPTs, i.e. at 2.5m depth. Based on the settlement estimates above, we would expect differential liquefaction settlements across the building footprint in the order of 100 to 150mm for the 67% design event defined above. Liquefaction in an event 33% of that defined for the ULS in NZS (PGA = g) is likely to be very limited, if it occurs at all. By inspection, the ground effects in a 1 in 500 year return period event will be worse than that for the 67% design event defined above. The PGAs and Magnitude used in the analyses are likely to be upper bound values. It s possible that a Site Specific Hazard Assessment could determine that the hazard is less than that suggested by NZS1170. Comparison to a corresponding PGA and representative Magnitude derived from the NZTA Bridge Manual (3 rd edition) 4 suggests that lower liquefaction potential is possible. 3 New Zealand Geotechnical Society (2010). Geotechnical Earthquake Engineering Practice, Module 1- Guideline for the identification, assessment and mitigation of liquefaction hazards. 4 New Zealand Transport Agency Bridge Manual 3rd Edition, SP/M/022, May // NZ // page 7

30 Lateral Spreading Although liquefaction is indicated in the 67% design event case considered, the variable nature of the soils identified suggests that liquefaction would likely be experienced in discontinuous zones, rather than as a uniform layer extending to the harbour to the west. We therefore consider that there is a low risk of lateral spreading towards the harbour occurring under the 67% design event case. Bearing Capacity Liquefaction is indicated from a depth of 2.5m below ground level. We understand that the buildings foundations are typically founded at a depth of around 1.0 to 1.5m below ground level. If liquefaction were to occur during a seismic event, then the potential exists for larger strains to be experienced under some foundations as a result of a loss of bearing support from the liquefied soils. The Administration building foundations are strip footings founded at around 1.5m below ground level. We note that the basement level around the stair lift shaft lies at around 2.5m below ground level, so could be directly bearing onto potentially liquefiable soils. This zone is the most likely to experience a loss of bearing support. By contrast buildings A and C are founded on pad foundations founded at around 1.5m below ground level. The consequence of a loss of bearing support under some foundations has been considered in the structural seismic assessments, refer to Structural System The lateral load resisting systems for Blocks A and C are identified to be: Longitudinal (north-south direction) Seismic loads in the lower two storeys are resisted by the perimeter reinforced concrete moment frame along Gridline I aided by the reinforced concrete moment frame along Gridline F for both Block A and C. A reinforcement concrete floor topping slab over Uni-span flooring transfers lateral seismic loads to the frames at levels 1 and 2. Block A seismic loads for the upper storey extension are resisted by plywood and plasterboard lined timber framed walls, and steel portal frames. Block C seismic loads for the upper storey extension are resisted by braced timber framed walls surrounding the stairs and elsewhere. Roof loads are transferred to walls via a plywood roof diaphragm for Block A and a steel bracing system for Block C. Transverse (east-west direction) Seismic loads in the lower two storeys are resisted by four reinforced concrete moment frames for Block A and three frames for Bock C. The remainder of the structure system is as for the north-south direction. Foundations Central columns are founded on large pad foundations. Perimeter columns are supported on a mix of pads and strip footings. Ground beams provide a tie between foundations. Columns Street frontage columns have been constructed with large false columns to the side of the core structural column. 20mm gaps are provided to the beams and footings, above and below // NZ // page 8

31 Walls Reinforced block walls are provided between some columns are ground floor. Separation has been provided to the columns. Figure 3 Typical Section Through Columns Along Street Frontages // NZ // page 9

32 3 Results of Seismic Assessment The results of our quantitative assessment of the structure for building Block A indicate the building achieves approximately 55%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170 The limiting mechanism for building Block A is identified as the lateral capacity of the timber wall bracing for upper storey extension, for shaking in the east-west direction. The upper storeys, although lighter than the lower storeys, are affected by amplification effects (refer 1.3) which result in seismic loading demand greater than the capacity of the wall bracing. The overall building seismic scores are limited by the lowest rated elements. The results of our quantitative assessment of the structure for building Block C indicates the building is likely to achieve greater than 67%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170 Table 1 presents the evaluated seismic performance in terms of %NBS of the individual structural systems in each loading direction. Table 1 - Summary of Seismic Performance of Structural Systems System Direction Seismic Performance in %NBS Notes Block A & C: Reinforced concrete frames Both >67%NBS Beam and column hinging. Block A & C: Cast-in-situ floor diaphragm Block A & C: Both >67%NBS Foundations Both >67%NBS Block A: Braced timber-framed walls Block C: Braced timber-framed walls Transverse (eastwest) Longitudinal (northsouth) Both ~55%NBS >67%NBS >67%NBS Assessed effect of loss of bearing support under one footing (one internal column and one corner column) Plywood & plasterboard linings Stairs Both >67%NBS Link bridges Both >67%NBS Assuming adjacent building movement is similar to Block A, and all ends constructed as per available details // NZ // page 10

33 4 Commentary on Associated Seismic Risks 4.1 Stairs The Department of Building and Housing issued Practice Advisory 13 in response to concerns about stair collapse and damage observed in the Christchurch earthquake. The primary concern of this Practice Advisory is staircases with sliding support details in mid to high-rise multi-storey buildings. We have assessed the expected performance of the stairs considering estimated building movements as defined by MBIE Practice Advisory 13. We believe the stairs are likely to remain available for egress for building drifts up to the level required by the advisory. Figure 4 Section Through Stairs 4.2 Link Bridges We have assessed the expected performance of the link bridges based on the available details and considering estimated building movements. We believe these can perform satisfactorily for the drifts we have calculated when the buildings area subject to 67% loading defined for the ULS event in NZS Figure 5 Link Bridge End Support Detail // NZ // page 11

34 4.3 Liquefaction Liquefaction is indicated from a depth of 2.5m below ground level. If liquefaction were to occur during a seismic event, the potential exists for a loss of bearing support to the pad foundations of Block A and C buildings. Our assessment shows that although there could be significant damage to the building in this event, the building is capable of maintaining structural integrity sufficient to achieve life safety objectives as defined by the NZSEE guidelines. 4.4 Risks from Non-structural Building Elements From our recent experience in evaluating similar buildings in Christchurch, non-structural building elements (façade glass, ceilings, internal walls, overhead services) constitute a significant proportion of the repair / reinstatement cost following an earthquake. In a moderate seismic event, some damage to non-structural elements would be expected. For a new building, full-height partitions (glazed or Gib-board lining), glazed street facades and ceilings are normally designed to accommodate the building s deformations Atrium Glazing We are concerned that the glazing in the atrium areas between the buildings, particularly at roof level, may be vulnerable to relative movement between the buildings during severe seismic shaking. If there is not suitable movement tolerance in this system, there may be a risk of shattered glass or glazing panels falling into the public access space below. We are in the process of engaging a glazing façade specialist to inspect the atrium glazing and report on the movement capability of the glazing system and the associated seismic performance. Figure 6 Atrium Glazing between Library and Blocks A & C // NZ // page 12

35 5 Assessment of Seismic Risk 5.1 Seismic Risk and Performance Levels In order to assess the seismic risk and performance of the atrium glazing, a specialist façade engineer is required. From our assessment, building Block A indicate the building achieves approximately 55%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade C building following the definition of the NZSEE building grading scheme. Grade C buildings have approximately 5-10 times the seismic risk compared to a new building, indicating a medium risk exposure. From our assessment, building Block C indicate the building achieves greater than 67%NBS in terms of the performance for life safety as determined using the NZSEE guidelines for an Importance Level 2 classification in accordance in with NZS1170. Therefore, it is a Grade B building or better following the definition of the NZSEE building grading scheme. Grade B buildings have approximately 2-5 times the seismic risk relative to a new building, indicating a low or medium risk exposure. The New Building Standard requires a building to have a low probability of collapse in a 1 in 500-year design level earthquake (ie. an earthquake with a probability of exceedance of approximately 10% over the assumed 50 year design life of a building). Building Grade Percentage of New Building Strength (%NBS) Relative Earthquake Risk Approx. Risk Relative to a New Building Risk Description A+ >100 <1 low risk A 80 to to 2 times low risk B 67 to 80 2 to 5 times low or medium risk C 33 to 67 5 to 10 times medium risk D 20 to to 25 times high risk E <20 more than 25 times very high risk A building achieving less than 34%NBS is categorised as an Earthquake Prone Building (EPB) and a building achieving less than 67%NBS is categorised as an Earthquake Risk Building (ERB). Block A and C buildings are not therefore categorised as an Earthquake Prone Building. Block A building is categorised as an Earthquake Risk building. The capacity of the building Block A is limited by a shortfall in the lateral capacity of the timber wall bracing for upper storey extension, limiting the seismic building score to less than 67%NBS for shaking in the eastwest direction // NZ // page 13

36 6 Seismic Retrofit and Strengthening 6.1 Retrofit and Strengthening Options The following seismic retrofit concept is to address the identified weakness in the lateral capacity of the timber wall bracing for upper storey extension to Block A. This concept has been developed for discussion with TCC. We propose replacement of the wall linings for five walls on the second floor of Block A. This would consist of the removal of existing plasterboard linings, installation of standard Gib system hold down fixings to studs and installation of plywood and plasterboard linings as required for the Gib BR7 system. This strengthening would raise the seismic performance of Block A to above 67%NBS as required by TCC. Figure 7 Proposed Wall Strengthening Block A Level Preliminary Cost Estimate Costs estimates of remedial conceptual designs are to be provided separately. 7 Next Steps In order to assess the seismic risk and performance of the atrium glazing, a specialist façade engineer is required. Beca do not have suitable expertise in this area so a specialist façade engineer is being engaged to carry out an assessment and report on this risk. This work is not complete at the time of writing. We recommend that TCC consider carrying out the following next steps: Carry out strengthening of the timber walls at level 2 of Block A in order to lift the building seismic score above the 67%NBS threshold identified by TCC. Further recommendations may be provided following completion of the glazing assessment work // NZ // page 1

37 Appendix A Sources of Information // NZ //

38 Sources of Information The following information was used to undertake the seismic assessment: Opus International Consultants Limited (2014). Tauranga City Council Civic Campus Structural Review Wharf Street and Willow Street Tauranga CBD. Prepared for Tauranga City Council. Documents obtained from Tauranga City Council comprising a set of scanned original Structural drawings. External and internal visual inspections of the building carried out on 20/02/2015. The following documents and references were available to undertake the seismic assessment: New Zealand Standard NZS1170 Structural Design Actions. New Zealand Standard NZS3101:2006 Concrete Structures Standard. New Zealand Standard NZS3404:2009 Steel Structures Standard. New Zealand Society for Earthquake Engineering (NZSEE) Guidelines on Assessment and Improvement of the Structural Performance of Buildings in Earthquake New Zealand // NZ //

39 Appendix B Seismic Assessment Assumptions // NZ //

40 Seismic Assessment Assumptions Seismic Loading The seismic design loads are determined in accordance with NZS1170.5:2004 with the following assumptions: Importance Level 2 structure (a normal use building) and a Design Life of 50 years. Site Location Tauranga Subsoil class category D. Only the Ultimate Limit State (ULS) is considered in the seismic assessment, which is concerned with life safety of the occupants and collapse prevention. Dead and Live Loads The following assumptions have been made in establishing dead loads for the structure: Reinforced concrete for floor slabs, columns, beams and walls is normal weight with a density including reinforcing of 2400 kg/m 3. Steel roof structure is a normal weight steel with a density of 7600 kg/m kPa of superimposed dead load for 1 st Floor, This includes 0.5kPa floor finishing and partitions and 0.5kPa for suspended ceilings, mechanical, electrical, plumbing, lighting, and miscellaneous. The superimposed dead load is assumed to be uniformly distributed over the floor plate. 0.6 kpa total dead load for the light-weight roof structure including steel trusses, assumed to be uniformly distributed over the floor plate. The live load assumption is based on NZS1170:2004 requirements: Ground Floor and 1st Floor: 3 kpa from Table 3.1, Type B, offices for general use. Roof 0.25 kpa from Table 3.2, Type R2, Other roofs. Assessment Assumptions The key assumptions made during our assessment were as follows: Item Assumption Comments Steel grades f y =275 MPa f y =380 MPa Concrete strength f c=25mpa Element Capacity Assessments Using probable material strengths and a hand analysis All longitudinal reinforcing bars for beams in the moment frames and at column longitudinal bars at column base. All longitudinal reinforcing bars for columns in the moment frames. Based on notes on the structural drawings. Typical for reinforced concrete moment resisting frames. This was carried out following the recommendations of the 2006 NZSEE Guidelines. Structural 3D Elastic Model in Analysis ETABS Diaphragms Rigid diaphragms Uni-slab floor diaphragm in level 1 and 2. Ply wood roof diaphragm in Block A. Steel roof bracing in Block C // NZ //

41 Item Assumption Comments Accidental Eccentricity Considered as part of ETABS analysis Modelling ETABS and SpaceGass models included rigid offsets The achievable seismic performance of the various structural elements can be estimated using the approach described in the 2006 NZSEE Guidelines. It assumes the Demand/Capacity ratio under the 100%NBS seismic forces (not factored by S p /k µ ) corresponds to the required ductility capacity (k µ ). The ratio of the available and the required ductility capacity is the approximate achievable seismic performance (in terms of %NBS). A Structural Performance Factor S p corresponding to the assumed ductility factor, k µ as per NZS is assumed. Seismic Mass The seismic mass is computed adopting the NZS1170.5:2004 loading combination W = G + Ψ E Q u = G + 0.3Q u. No area reduction factor is used to calculate the ultimate live load Q u, as a conservative assumption. The additional floor seismic mass (excludes the self-weight of the members) is distributed equally to each node at the floor level in the computer model. The self-weight of the members is computed directly by the programme // NZ //

42 Appendix C Building Inspection Photographs // NZ //

43 Seismic Assessment - Willow Street Campus - Building A & C Building Inspection Photographs Figure 8 Examples of Columns with fake column Sections Figure 9 Typical Beam Column Junction Internal to Frame and on Corner // NZ //

44 Seismic Assessment - Willow Street Campus - Building A & C Figure 10 Low Level Walls Between Frames on South and West Elevations st nd Figure 11 Pedestrian Bridges between Blocks at 1 and 2 Floor Levels // NZ //

45 Seismic Assessment - Willow Street Campus - Building A & C st nd Figure 12 Pedestrian Bridge Supports at 1 and 2 Floor Levels Figure 13 Roof Structure Between Library and Blocks A & C // NZ //

46 Appendix D Structural Drawings // NZ //

47 End of Seismic Assessment Willow Street Campus Building A & C Report (20 March 2015) Beca // 10 April // NZ // page 13

48 Appendix C Plan of Opus Test Locations Beca // 10 April // NZ // page 11

49 CPT03 Administra on Building CPT04 & Shear Wave Test CPT05 Baycourt TCC Library & Offices CPT01 CPT02 Key CPT test loca on (approximate loca on) Contours APPENDIX A: TESTING LOCATION PLAN 104/2014 SCALE 1:NTS 29B302_00

50 Appendix D Overall Site Plan Beca // 10 April // NZ // page 12

51 D Drawing Originator: Original Scale (A1) Reduced Scale (A3) Design Drawn Dsg Verifier Dwg Check Approved For Client: Project: Construction* Date Title: Discipline Drawing No. Rev. BLUEBEAM No. Revision By Chk Appd Date * Refer to Revision 1 for Original Signature DO NOT SCALE IF IN DOUBT ASK.