Detailed Assessment of St. Patrick Church, Paraparaumu, NZ. 09 January 2013 MIL Phase 05

Transcription

1 Detailed Assessment of St. Patrick Church, Paraparaumu, NZ 09 January 2013 MIL Phase 05

2 Report Tracking Miyamoto Impact Ltd. External Review Revision Status Date Prepared by Checked by Review Date Reviewed by 001 Draft 29/11/12 K Wong M King 20/12/12 CBPL 002 Final 09/01/13 K Wong M King Miyamoto Impact Total Seismic Solutions Level Victoria Street Wellington Miyamoto Impact, All rights reserved. This report or any part thereof must not be reproduced in any form without the written permission of Miyamoto Impact.

3 Table of Contents Executive Summary... 2 Background Information... 4 Findings... 5 DDD Assessment... 6 Solutions... 6 Conclusions and Recommendations... 8 Appendix A: Abbreviations Appendix B: Assumptions Appendix C: Preliminary Calculations Appendix D: Preliminary Strengthening Sketches 2013 Miyamoto Impact P a g e 1 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

4 Executive Summary In response to a request by the Archdiocese of Wellington, Miyamoto Impact has performed a Detailed Assessment (DA) of St. Patrick s Church in Paraparaumu, New Zealand. The purpose of this evaluation is to determine the viability of restoring occupancy to the church. We have performed a DA of the building, determined if any critical structural weaknesses in the seismic load resisting system exist, and provided recommendations for further action. The single storey parish church was constructed in 1964, and is located at 16 Hinemoa Street in Paraparaumu, a highly seismic zone of the Wellington Region. A site survey of the church was performed on 8 November, 2012, which included visual observations of the building s interior and exterior. Our evaluation of the existing structure included an assessment of specific building characteristics in conjunction with a site survey. A preliminary analysis of key elements of the seismic force resisting system has been performed. The Critical Structural Weaknesses associated with site and building characteristics have been taken into account. Deficiencies were found in several locations, the most serious being the longitudinal shear walls, at 9%NBS. The following table summarises the seismic deficiencies and CSWs encountered, their impact and the recommended solution. Deficiencies and Critical Structural Weakness Diaphragm Capacity Shear Wall Capacity Out-of-Plane Wall Anchorage Impact Inability to distribute the building s seismic mass to the resisting shear walls Inability to resist the seismic induced forces generated by the building s mass Un-braced partial-height walls may tilt or collapse, leading to shear wall failure Comments and Solutions Install higher capacity roof sheathing Install plywood sheathing and infill selected windows Install horizontal beams along the walls and spanning between existing steel portal frames The previous IEP report by Clendon, Burns & Park, Ltd concluded that the building is at 9% of New Building Standard (%NBS) thus classifying the structure as Earthquake Prone. Our Detailed Assessment confirms the low classification of the building, showing that some critical structural elements have strengths as low as 7%NBS. By strengthening the existing building as noted above, most seismic deficiencies would 2013 Miyamoto Impact P a g e 2 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

5 be mitigated and the seismic performance of the rehabilitated building would vastly increase. The rehabilitated building could be classified as meeting at least 67% NBS. Preliminary strengthening sketches are included in Appendix D. Should the Archdiocese decide to proceed with seismically strengthening this building, a program of geotechnical investigation, exploration of hidden portions of the building, and material sampling and testing may be warranted to gather additional information to aid in the development of an optimum strengthening solution. Michael King MIPENZ, CPEng Structural Engineer for Miyamoto Impact MKing@miyamotointernational.com Ken Wong SE (CA USA) Structural Engineer for Miyamoto Impact KWong@miyamotointernational.com 2013 Miyamoto Impact P a g e 3 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

6 Background Information St. Patrick s Church is a one-story parish church located at 16 Hinemoa Street in Paraparaumu, a highly seismic zone of the Wellington Region. The church, which is situated between residential houses, measures approximately 830 square metres in area with overall plan dimensions of approximately 36 metres long by 28 metres wide. The building consists of a large worship area, small ancillary rooms, and a small balcony. For purposes of this report, the main entry of the building will be considered to be facing north. A site survey of the church was performed on 8 November 2012, which included visual observations of accessible portions of the building s interior and exterior. The facility was designed in 1964 and features a long-span steeply pitched roof, a high, open ceiling, a large window at the north gable end and vertical windows along the east and west sides of the worship area. The building is roughly T-shaped in plan, with the roof at the north end being both wider and higher than the main roof. Roofing is composed of concrete tile, and roof framing appears to be composed of straight sheathing over timber joists, which span between exposed steel portal frames. Exterior walls are of mixed timber and concrete masonry construction, with masonry typically extending from the floor level up to a height of 1.85m, and timber walls above. The exception to that is at the north wall, which is constructed in masonry up to the height of the balcony. Seismic loads in the east-west (across) direction are resisted by bending of the steel portal frames. Seismic loads in the north-south (along) direction are resisted by the exterior walls of the main worship area. Prior to this Detailed Assessment (DA), an Initial Evaluation Procedure (IEP) had been completed by Clendon Burns & Park Ltd on 27 June The IEP concluded that the church was at 9% of New Building Code (%NBS), this classifying the structure as an Earthquake Prone Building as outlined in the New Zealand Society of 2013 Miyamoto Impact P a g e 4 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

7 Earthquake Engineering s Assessment and Improvement of the Structural Performances of Buildings in Earthquakes. The building is used as a church; therefore, the seismic assessment was performed for an Importance Level 3 associated with buildings with capacities greater than 300 people. Site specific geotechnical information was not available for review. Therefore, subsoil Type C was used based on obtained information from the IEP Report. Findings Our evaluation of the existing structure included an assessment of specific building characteristics in conjunction with our visual observation of the current conditions. In order to identify potential seismic deficiencies associated with the existing building, a preliminary analysis of key elements of the seismic force resisting system has been performed based on earthquake actions in accordance with the New Zealand Standard (NZS) seismic vulnerabilities, and Critical Structural Weaknesses (CSW), associated with site and building characteristics has been taken into account in accordance with NZSEE s Assessment and Improvement of the Structural Performance of Buildings in Earthquakes. Plan showing %NBS of critical components 2013 Miyamoto Impact P a g e 5 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

8 Per our analysis, the building appears to generally satisfy the target performance level of 67%NBS in the across (East-West) direction but is deficient in the along (North-South) direction. Critical areas of concern are the diaphragm over the south roof (40%NBS) and all north-south shear walls (9% to 19%NBS). The poor rating of the N-S walls is partly due to the size and pattern of window openings. The windows are tall and closely spaced, so that the solid walls between them are generally too slender to be considered effective as shear walls. An additional area of concern is with the out-of-plane bracing of the partial-height masonry walls. These walls are not braced against seismic loads on their faces, and may collapse or tilt strongly in an earthquake. Their loss will also weaken the timber walls which rest on them, causing further damage. DDD Assessment The death, damage, and durability (DDD) assessment is an estimation of death, sustained building damage, and construction durability likely to result following a severe seismic event. Historically, single storey timber framed buildings have generally performed well in past earthquake events. Their performance is greatly dependent on occupancy; buildings such as houses that have many interior walls have generally shown reasonably high performance even when they were not intentionally designed to resist earthquakes. Unlike most houses, a church building typically has large assembly rooms and has few interior walls, and are is more vulnerable to seismic induced damage unless properly designed. Given the seismic deficiencies and CSW noted in the previous section, it is likely that the building will sustain moderate damage (i.e. extensive cracking of ceiling and wall finishes; distorted window and door openings; cracking of foundations; significant differential settlement of underlying soil; loss of some utilities, etc.). The occupants of this building are likely to evacuate with some injuries but major fatalities are not anticipated. There is a direct correlation between anticipated damage and durability. Given the damage likely to occur, it is expected this construction will not be highly durable in the event of a severe earthquake. Solutions Based on preliminary analysis, the seismic deficiencies of St. Patrick s Church can be mitigated by strengthening the exterior walls and the south portion of the roof diaphragm. The strengthening of the walls involves installation of the following structural elements: Plywood sheathing on the exterior stud walls. Because of the high loading placed on the shear walls, we expect that they will need to be sheathed on both interior and exterior faces. Alternatively, some windows can be in-filled to lengthen the walls Miyamoto Impact P a g e 6 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

9 Additional anchor bolts to anchor the timber shear walls to the partial-height masonry walls below. Tie-down anchors epoxied into the masonry at the ends of shear walls to prevent the walls from overturning. Nailed or screwed steel straps around windows, doors and other large openings to prevent localised failures. Similarly, seismic strengthening of the roof involves installation of the following components: Plywood sheathing over the existing roof framing. Strengthening of splices in the existing wall top plate. Lastly, the partial height masonry walls can be braced by installing horizontal steel beams between the existing steel portal frames. These would run along the walls slightly below the window sills; epoxy bolts can be used to anchor the walls to the beams. Such a strengthening scheme could be carried in a phased manner to allow the church to maintain operation. Refer to preliminary strengthening sketch found in appendix D. The following table summarises the structural deficiencies observed, their impact and our proposed solution: Deficiencies and Critical Structural Weakness Diaphragm Capacity Shear Wall Capacity Out-of-Plane Wall Anchorage Impact Inability to distribute the building s seismic mass to the resisting shear walls Inability to resist the seismic induced forces generated by the building s mass Un-braced partial-height walls may tilt or collapse, leading to shear wall failure Comments and Solutions Install higher capacity roof sheathing Install plywood sheathing and infill selected windows Install horizontal beams along the walls and spanning between existing steel portal frames 2013 Miyamoto Impact P a g e 7 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

10 Conclusions and Recommendations The previous IEP report concluded that the building is at 9%NBS thus classifying the structure as Earthquake Prone per NZSEE s Assessment and Improvement of the Structural Performance of Buildings in Earthquakes. Findings from this DA confirm and outline the deficiencies and CSWs encountered and likely death, damage, and durability to be expected following a severe seismic event. By strengthening the existing building as noted above, mitigation of most seismic deficiencies would occur and the seismic performance of the rehabilitated building would vastly increase. The rehabilitated building could be classified as meeting at least 67% NBS. Should the Archdiocese decide to proceed with seismically strengthening this building, a program of geotechnical investigation, exploration of hidden portions of the building, and material sampling and testing may be warranted to gather additional information to aid in the development of an optimum strengthening solution Miyamoto Impact P a g e 8 Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

11 Appendix A: Abbreviations CSW DA DDD IEP - Critical Structural Weakness - Detailed Assessment - Death, Damage, Durability - Initial Evaluation Procedure NZSEE - New Zealand Standards of Earthquake Engineering %NBS - New Building Standard Percent 2013 Miyamoto Impact Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

12 Appendix B: Assumptions - Perimeter walls are assumed to be framed with Gypsum wall board in order to calculate the shear capacity of the walls using the NZSEE Miyamoto Impact Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

13 Appendix C: Preliminary Calculations 2013 Miyamoto Impact Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

14 Action (Load) Takeoff Project: Paraparaumu Church Sheet No. Project No: MIL Calc. By: JL Date: 12/4/12 Chk. By: Date: (E) Roof Item Gravity Roofing mm Straight sheathing 0.10 Purlins 0.07 Finish 0.30 Miscellaneous 0.23 Σ DL 1.10 kpa Imposed Actions (Live Load) Roof 0.5 kpa (E) Timber Wall Item Gravity 200 mm Timber Wall 0.10 Finish 0.35 Miscellaneous 0.05 Σ DL 0.50 kpa (E) Masonry Wall Item Gravity 215 mm Masonry Wall 3.60 Finish 0.25 Miscellaneous 0.05 Σ DL 3.90 kpa Paraparaumu Church NZ Earthquake Action

15 Project: Paraparaumu Church Sheet No. Project No: MIL Calc. By: JL Date: 12/4/12 Chk. By: Date: Equivalent Static Method - NZS :2004 Design Earthquake Actions Horizontal Siesmic Shear Structural & Site Specific Information Project Address = 16 Hinemoa Street, Paraparaumu Height to Roof above Seismic Base h n = 4.5 m Seismic Force Resisting System = Concrete Masonry Wall/Timber Wall Number of stories = 1 Structural Ductility Factor μ = 2.00 Building Period Coefficient k t = (NZS Supp 1: 2004 Clause C & C ) Site Class = C Period, ULS T 1, u = s Period, SLS T 1, s = s Site Spectra Parameters Spectral shape factor C h (T) = 2.36 g (Table 3.1) Hazard Factor Z = 0.40 (Table 3.3) Distance to nearest fault D = 14 (Table 3.3) Required annual probability of exceedence 1/1000 Return Period Factor, ULS R u = 1.30 (Table 3.5) Return Period Factor, SLS R s = 1.30 (Table 3.5) Maximum Near-Fault Factor N max (T) = 1.20 (Table 3.7) Near Fault Factor N(T,D) = 1.07 (Clause 3.1.6) Elastic Site Hazard Spectrum, ULS C(T) u = 1.31 g (Clause 3.1.1) Elastic Site Hazard Spectrum, SLS C(T) s = 1.31 g (Clause 3.1.1) Horizontal Design Action Ultimate Limit State Structural Performance Factor, ULS S p, u = 0.7 Structural Performance Factor, SLS S p, s = 0.7 k μ, u = 1.57 (Clause ) k μ, s = 157(Cl 1.57 (Clause ) 5211) Horizontal Action, ULS C d (T 1 ) u = 0.58 (Eq. 5.2 (1)) C d (T 1 ) min, u = 0.05 (Eq. 5.2 (2)) C d (T 1 ) min, u = 0.04 (Eq. 5.2 (2)) Horizontal Action, SLS C d (T 1 )s = 0.58 (Eq. 5.2 (1)) C d (T 1 ) min, s = 0.05 (Eq. 5.2 (2)) C d (T 1 ) min, s = 0.04 (Eq. 5.2 (2)) Horizontal Design Action, ULS C d (T 1 ) u = 0.58 Horizontal Design Action, SLS C d (T 1 ) s = 0.58 Paraparaumu Church NZ Earthquake Action 2 / 6

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33 Appendix D: Preliminary Strengthening Sketches 2013 Miyamoto Impact Detailed Assessment of 16 Hinemoa Street, Paraparaumu, New Zealand

34 STEEL BEAM AT WINDOW SILL PLYWOOD SHEAR WALLS A PLYWOOD ROOF DIAPHRAGM STRENGTHENING PLAN EXISTING COLUMN NEW BEAM ANCHOR PLATE WITH BOLT TO MASONRY ELEVATION "A" NEW BEAM AT WALL