REPORT PREPARED FOR Monterey Avenue Palm Desert, CA Peters Canyon Rd., Suite 140, Irvine, CA IDS Project Number 11.

Transcription

1 REPORT STRUCTURAL ENGINEERING ASSESSMENT OF THE COLLEGE OF THE DESERT HILB STUDENT CENTER LIBRARY CONVERSION PREPARED FOR COLLEGE OF THE DESERT Monterey Avenue Palm Desert, CA BY 1 Peters Canyon Rd., Suite 140, Irvine, CA IDS Project Number April, 2011

2 TABLE OF CONTENTS Page I. EXECUTIVE SUMMARY... 3 II. INTRODUCTION Background... 5 Purpose... 6 Scope... 6 Limitations... 6 III. REFERENCES... 7 IV. BUILDING DESCRIPTION General Description... 7 Vertical Load Carrying System... 7 Lateral Force Resisting System... 8 V. SEISMIC EVALUATION Seismic Hazards... 8 Seismic Activity Near the Campus ASCE 31 Tier 1 Evaluation Results Seismic Performance VI. LIBRARY CONVERSION EVALUATION...15 VII. SITE OBSERVATIONS VIII. FINDINGS & RECOMMENDATIONS Possible Retrofit Concepts for Seismic Performance Possible Retrofit Concepts for Library Loading Opinion of Probable Cost APPENDICES A ASCE Tier 1 Evaluation Checklists Page 2 of 31

3 STRUCTURAL ENGINEERING ASSESSMENT OF THE COLLEGE OF THE DESERT HILB STUDENT CENTER LIBRARY CONVERSION I. EXECUTIVE SUMMARY: This report presents the results of the structural engineering assessment of the Hilb Student Center at the College of the Desert campus in Palm Desert, California. This assessment includes a seismic hazards assessment, an evaluation of structure performance in the event of a major earthquake, and an evaluation of the structure s capacity for conversion to library usage in accordance with current code requirements. The evaluation of nonstructural systems, including anchorage and bracing of walls, ceilings, equipment and utility systems is outside the scope of this project. The Hilb Student Center is a reinforced concrete building. It is a high bay structure with interior open spaces visible to the raised roof area. The interior open spaces are surrounded by partial mezzanine areas. The total existing floor area of this building including the basement level is approximately 18,000 square feet. The facility was designed circa The College of the Desert campus is located between the San Andreas and San Jacinto fault systems. The campus is within 8 miles of the San Andreas fault, which is believed capable of a magnitude 8 event and 19 miles from the San Jacinto fault which is believed capable of a 7.5 event. Numerous other fault zones capable of causing strong ground shaking are located within close proximity to the campus. Ground shaking is believed to be the most significant seismic hazard to the site. In addition, the potential for seismically induced settlement is considered high. Since a geotechnical investigation is required to quantify the potential for seismic settlement at the specific Hilb Center site, the seismic risk and possible damage scenarios described herein are based only on the ground shaking hazard. It does not appear that surface fault rupture, lateral spreading, liquefaction, landslides and other soils effects are likely to occur at this site. Seismic Performance and Retrofit Evaluation The seismic risk assessment is based on an ASCE 31 Tier 1 vulnerability analysis conducted via checklists of critical structural items for this building type, in conjunction with a review of original design drawings and assessment of potential damage areas based on experience and judgment concerning the performance of this type of structure in past major earthquakes. ASCE 31 is a national document widely used for the seismic assessment of building structures as adopted by DSA for building assessment. Based on the ASCE 31 Tier 1 analyses, and review of original structural design drawings, we find the following areas of potential damage and associated proposed retrofit measures are required in order to bring the building into conformance with DSA s Enhanced Life Safety performance goals for community college facilities that house classrooms and student activities. Strengthen High Roof Columns Install Steel Braced Frames at Building Corners Page 3 of 31

4 Strengthen Main Roof Diaphragm Install Main Roof Chords and Collectors Library Conversion Evaluation The ground floor slab over the basement, the mezzanine slabs, and selected columns and foundations were evaluated for current code library floor loading requirements, which include live loads of up to 150 pounds per square foot of floor area. Based on our analyses, we found two areas of deficiency with corresponding retrofit requirements: Five areas of the ground floor slab over the basement have inadequate top reinforcing at the supporting column locations. Correction of this deficiency could involve applying glass or carbon fiber reinforced polymer to the top of the concrete floor slab in zones of inadequate reinforcing. The cantilever slabs at the perimeter of the mezzanine have excessive deflection, and the slab at the cantilever-support columns is subject to punching shear. In order to efficiently correct these two deficiencies with a single corrective measure, 8 inch thick by 6 foot square concrete column drop caps can be constructed at the underside of the slabs at each column. Retrofit Costs Our opinion of the probable cost to implement the above recommendations as further described in this report is $1,830,000. This cost covers seismic upgrade of the building structure, plus upgrade of structural floor areas to accommodate library floor loading as follows: $1,559,000 for seismic upgrade and $271,000 for library upgrade. It is assumed for cost purposes that the building will be closed during construction, thus allowing for uninhibited access to perform the structural work. Page 4 of 31

5 II. INTRODUCTION: Background: The Hilb Student Center, located on the College of the Desert campus at Monterey Avenue in Palm Desert, California is a two-story building with partial mezzanine and partial basement. The Hilb Student Center was originally constructed circa 1961 as the campus Library and is now being reevaluated for potential library usage in conformance with current code requirements for gravity and seismic loading. The location of the Hilb Student Center building is redlined on the campus map shown in Figure 1. Figure 1. Hilb Student Center Location Page 5 of 31

6 Purpose: This report primarily summarizes the results of site observations, drawing reviews, and preliminary projections of structural performance during a major earthquake based on engineering judgment in conjunction with ASCE 31 [Ref. 1], Tier 1 seismic evaluation checklists. ASCE 31 is a national document widely used for the seismic assessment of building structures as adopted by DSA for building assessment. The report includes a summary of project results, as well as recommendations, preliminary costs for seismic retrofit and library use upgrade, and recommended next steps. Scope: The project scope of provided services is as follows: 1. Review available structural and architectural drawings and visit the project site. 2. Determine the regional seismic hazard and assess the potential for structural damage. 3. Perform an ASCE 31 (FEMA 310) Tier 1 evaluation 4. Assess the capacity of the existing structure to support library floor loading and seismic forces in accordance with current code requirements. 5. Prepare a summary report with strengthening recommendations, preliminary retrofit sketches, and an opinion of probable cost for the retrofit construction. Limitations: This report is based on a site visit, review of available drawings and structural screening and preliminary evaluation based on judgment and experience. This assessment is based on the assumption that the building was constructed in accordance with the available existing drawings and that elements used to resist lateral forces are in good condition. Our investigation was limited to the visual observation of items not covered by finish material. Other conditions affecting the structure that were not inspected, anticipated, or accessible are beyond the scope of this report. This assessment is limited to the buildings primary structural systems. Evaluation of nonstructural items such as architectural elements, furnishings and interior equipment, and electrical, mechanical, and plumbing systems are not considered in this evaluation. The findings presented in this report are for the sole use of the College of the Desert in its evaluation of the seismic performance of the subject buildings, and are not intended for use by other parties, and may not contain sufficient information for purposes of other parties or other uses. Our professional services have been performed with the degree of care and skill ordinarily exercised, under similar circumstances, by reputable consultants practicing in this field at this time. Page 6 of 31

7 III. REFERENCES: The following references were used in the evaluation of this building: 1. American Society of Civil Engineers; ASCE/SEI 31-03, Seismic Evaluation of Existing Buildings. 2. Johnson & Nielsen Structural Engineers; Library, College of the Desert, Coachella Valley Junior College District, Riverside County, California; Sheets S1 to S9 (Approved 07/18/1961), Sheets S1A, S2A, S5A (Approved 05/22/1964). 3. City of Palm Desert; Comprehensive General Plan; Adopted March 15, USGS, Fault Map, 5. International Conference of Building Officials; Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada; February, Southern California Earthquake Data Center (SCEC), Faults of Southern California: 7. USGS, Intensity Map for Landers Earthquake, 8. USGS, Intensity Map for Hector Mine Earthquake, IV. BUILDING DESCRIPTION: General Description: According to available structural drawings [Ref. 2], this building has approximate dimensions of 120 feet (east-west) by 150 feet (north-south). The roof and mezzanine are approximately 28 feet and 13 feet above the ground level, respectively. In addition, there is small raised center portion of roof. The approximate building area is 18,000 square feet with an additional 10,500 square feet at the mezzanine and 8,500 square feet at the partial basement. Vertical Load Carrying System The roof consists of 6-inch thick precast concrete panels supported by concrete beams spaced at 15 feet on center each way. The beams are typically arched and vary in depth from 17 inches at midspan to 40 inches at their supports. The beams are supported by 18-inch square columns, which taper near the top. The mezzanine floor and ground floor above the basement portion consist of 8-inch cast-in-place, two-way concrete slabs supported by concrete columns and walls below. The foundations consist of spread footings at columns and continuous footings around the perimeter and basement walls. The ground floor consists of a 4-inch thick concrete slab-on-grade with welded wire mesh reinforcing. Page 7 of 31

8 Lateral Force Resisting System The Hilb Student Center relies on steel decking at the high roof to transfer forces to the non-ductile beam-column frames that transfer the forces down to the main roof level. At the main roof, precast concrete panels transfer lateral forces to the vertical lateral-force-resisting-system consisting of concrete shearwalls. The existing configuration has no shearwall on the west side of the building. The mezzanine slab also acts as a diaphragm to distribute forces to the perimeter concrete shearwalls below. The concrete walls and entry level floor slab together transfer forces to the foundations, where the soils resist them. V. SEISMIC EVALUATION: Seismic Hazards: The following is an overview of the key seismic hazards for the College of the Desert campus. The campus is located in the city of Palm Desert between two major fault systems [Refs. 3, 4, 5] - the San Andreas fault and the San Jacinto Fault. These fault systems, described in the paragraphs below, are considered most likely to significantly affect the campus with as high as 8 magnitude earthquakes. Another significant fault that could potentially affect the site is the Elsinore faults system. See Figure 2 for a map of faults in the vicinity of the Campus [Ref. 6]. Based on the Palm Desert General Plan [Ref. 3], ground shaking is expected to be the most significant and probable seismic hazard to the site. Seismically induced settlement as well as landslides could be triggered by strong ground shaking causing damage to subsurface structures (See Fig. 3, Ref. 3 indicating the Campus is in a zone of high seismic settlement probability). Based on the sediment type at the site, liquefaction hazard is possible only if the ground table rises to within 50 feet of the ground surface. Detailed geotechnical studies are required to quantify the seismic settlement hazards as well as projections of ground water locations and influence on liquefaction potential during a major earthquake. There are no active or potentially active faults on the campus, which is not located within a currently designated State of California Earthquake Fault Zone. Listed below and shown in Figure 2 are several faults of varying significance in terms of potential for causing significant shaking at the College of the Desert campus: 13 km (8 mi) San Andreas Fault (southern segment) [Ref. 5] 30 km (19 mi) San Jacinto Fault [Ref. 5] 48 km (30 mi) Elsinore Fault [Ref. 3] Page 8 of 31

9 College of the Desert Elsinore Fault San Andreas Fault System Coachella Segment San Jacinto Fault System Figure 2: USGS Vicinity Map of Faults Page 9 of 31

10 Figure 3: Seismically Induced Settlement (Ref. 3) College of the Desert Major faults that could affect the College of the Desert campus: San Andreas Fault System [Ref. 6] TYPE OF FAULTING: Right-lateral strike-slip LENGTH: 550 km for the southern (Mojave) segments LAST SIGNIFICANT QUAKE: January 9, 1857 SLIP RATE: 25.0 to 35.0 mm/yr INTERVAL BETWEEN MAJOR RUPTURES: Average of 140 years on the southern segment PROBABLE MAGNITUDES: M W OTHER NOTES: The San Andreas is perhaps California s most significant fault zones, extending from south of the Salton Sea through Central California and off the coast north of San Francisco. Scientists consider this fault as a series of individual fault segments. The southern series of these segments are most likely to affect the college site. San Jacinto Fault System [Ref. 6] TYPE OF FAULTING: Right-lateral strike-slip, minor right reverse LENGTH: 210 km Page 10 of 31

11 MOST RECENT MAJOR RUPTURE: Within the past couple 100 years SLIP RATE: 7 to 17 mm/yr INTERVAL BETWEEN MAJOR RUPTURES: Between 100 and 300 years PROBABLE MAGNITUDES: M W Elsinore Fault System [Ref. 6] TYPE OF FAULTING: right-lateral strike-slip LENGTH: 180 km MOST RECENT MAJOR RUPTURE: May 10, 1910 SLIP RATE: 4 mm/yr INTERVAL BETWEEN MAJOR RUPTURES: approximately 250 years PROBABLE MAGNITUDES: M W OTHER NOTES: The Elsinore fault zone is one of Southern California s most significant, although recently it has not been as active. The Laguna Salada fault, which is its southeastern extension, ruptured in 1892 in a magnitude 7 earthquake. Seismic Activity Near the Campus: Seismic intensity is a measure of the ground motion felt during a seismic event. Intensity depends on proximity to the source, soil conditions and other factors. Accelerographs, which measure ground shaking, have been installed by the California Geological Survey throughout the state, from which vital information such as seismic intensity is obtained during seismic events. Shakemaps illustrate these recorded ground motions. The College of the Desert campus is located in the vicinity of two large and relatively recent earthquakes: the 1992 Landers and the 1999 Hector Mine earthquakes. Figures 4 and 5 below show the perceived ground shaking and estimated peak ground acceleration (pga) [Refs. 7, 8]. Both figures show that the campus was in an area that likely experienced moderate to strong shaking during the two earthquakes. However, we have been informed that there was no significant structural damage observed at the campus as a result of these events. Page 11 of 31

12 College of the Desert Figure 4: Seismic Intensity Map for the Landers Earthquake, June 1992 Page 12 of 31

13 College of the Desert Figure 5: Seismic Intensity Map for the Hector Mine Earthquake, October 1999 Page 13 of 31

14 ASCE 31 Tier 1 Evaluation Results: Based solely on the checklists presented in Appendix B as excerpted from Reference 1, we find that there are significant deficiencies within the Hilb Student Center building that could lead to serious structural damage during a strong regional earthquake with the code-expected ground shaking in the Palm Desert area. This damage could be greatly enhanced by relative settlements in the building that may occur due to seismically induced building settlements as indicated by the City of Palm Desert General Plan. Without the benefit of a Geotechnical investigation for the specific purpose of quantifying the potential settlement hazard, it is not possible to reliable predict settlement effects on the building. Thus, the potential damage and areas recommended for seismic retrofit are based only on the ground shaking hazard. The following is a brief summary by building of the Tier 1 evaluation results: Concrete Columns Above Main Roof - The concrete columns lack sufficient strength, stiffness and ductility to resist lateral forces at the high roof and transfer them to the main roof level below. Moment frames Above Mezzanine - The concrete columns, beams and their connections lack strength, stiffness and ductility to resist lateral forces at the main roof level and transfer them to the mezzanine level below. Shearwalls Above the Mezzanine - There are three cast-in-place concrete shearwalls located at the north, east and south sides of the structure. Since there is not a shearwall at the west side of the building above the mezzanine, the shearwall layout is poor and is expected to cause large torsional displacements and forces during a major earthquake. Furthermore, the connections of these walls to the main roof elements are not adequate. Collectors at the Shearwalls Above the Mezzanine - There are no elements to collect lateral forces from the roof diaphragm to the three concrete shearwalls mentioned above. Chords at the Main Roof - Existing reinforcing at the perimeter concrete beams is not adequate to resist the expected chord forces around the exterior boundary of the roof diaphragm. Precast Panel Connections at Main Roof Level - Further evaluation and analysis is recommended for the main roof level diaphragm since it relies on connections between individual precast concrete panels to properly distribute forces to the vertical elements of the lateral-force-resisting-system below. Precast Cladding Connections - Further inspection, evaluation and analysis are required for the connections of the precast concrete cladding panels at the main roof level. Also, no information was available regarding the concrete plank screens at the exterior of the screen walls at the stairs. Seismic Performance: The overall seismic evaluation included a site visit, a review of available drawings [Ref. 2], Tier 1 and limited Tier 2 evaluation of potential seismic deficiencies using ASCE 31 [Ref. 1] (see above paragraph), judgment and experience in investigation of past earthquake performance and research for Page 14 of 31

15 similar buildings. A detailed assessment of nonstructural components is beyond the scope of this project. The performance level used in this evaluation was Enhanced Life Safety in order to meet DSA s expectations for somewhat better performance than that provided by minimal life safety provisions. As defined by ASCE 31, the minimum Life Safety level is a level of performance that includes damage to both structural and nonstructural components during a design earthquake, such that (a) partial or total structural collapse does not occur, and (b) damage to nonstructural components is nonlife-threatening. The enhanced life safety performance level allows for some minor but significant damage to the structure, with the intent that occupants of the building will be able to exit the facility safely following a major seismic event. Existing Conditions: A brief overview of the anticipated seismic performance of the Hilb Center is given below. Note that this building was approved for construction in This date is noteworthy as it means that construction was likely completed prior to the San Fernando earthquake of February 9, In this earthquake, many buildings similar to in construction to the Hilb Center were heavily damaged. As a result of this damage, there were significant design practice and building code changes directly applicable to much of the design and detailing shown on the record drawings for this building. As indicated above, the building was designed and constructed in the circa mid-1960s timeframe. At this time in the evolution of building codes and structural design practice in earthquake areas, particularly in Southern California, research into design of concrete structures to be ductile (i.e. resistant to sudden failure following initial seismic induced damage such as cracking and spalling) was in its infancy, and code requirements were not in place. This all changed as a result of the severe damage to and collapse of concrete buildings and bridges in the 1971 San Fernando ( Sylmar ) earthquake. Following the San Fernando quake, much research took place and the building codes (e.g. UBC) and materials design publications (e.g. ACI 318 for concrete) were updated to include provisions for making concrete structures ductile i.e. resistant to failure or collapse after the onset of damage due to strong shaking. Buildings of the Hilb Center s vintage tend to be vulnerable to significant structural damage because they were designed for far less seismic loading than modern codes prescribe, and the detailing of load transfer points and connections in these older buildings does not reflect the lessons learned from the 1971 San Fernando and later earthquakes, and the ensuing research and code changes. In light of these conditions, and the results of the Tier 1 analyses described above, we find that the Hilb Center has significant deficiencies as noted by the ASCE 31 Evaluation Results above that we recommend for further analysis and possible strengthening. VI. LIBRARY CONVERSION EVALUATION: Scope: For the purposes of this evaluation, a uniform live load of 150 psf based on the 2010 California Building Code (CBC) was applied to the ground floor and mezzanine levels. At this time, detailed information on library stacks, corridors and reading rooms was not available, so the 150 psf is a reasonable and conservative value. Once a proposed layout of library features is prepared, a more Page 15 of 31

16 detailed analysis involving specific loading requirements can be performed; i.e., stack areas involve a 150 psf loading requirement; corridors must be designed for 80 psf; and reading rooms are designed for 60 psf. Note that the use of a uniform load of 150 psf for checking/upgrading structure capacity allows for maximum future flexibility in locating/relocating stack areas without regard to floor capacity. Analysis Methods: For floor slab analyses, a SAFE computer model was generated for the ground floor elevated slab areas over the basement, and for the mezzanine floor areas. Manual calculations were performed in order to confirm computer output results for stress and deflection checks of the ground floor and mezzanine slabs. Manual analyses in conjunction with spreadsheet software were used to check the capacity of key columns and their foundations. Critical Structural Features: The following is an overview of the key structural information extracted from the record drawings. This information was used in evaluating the capacity of main structural floor slabs, columns and foundations to resist the proposed library loading. Ground Floor Slab over Basement: The ground floor slab is composed of 8 inch thick concrete with fc of 3,000 psi, and grade 40 reinforcing bars with fy = 40,000 psi. Typical reinforcing for the ground floor slabs is #5 at 12 inches each way, top and bottom; with additional top and bottom reinforcement at specific locations. Mezzanine Floor: The mezzanine floor slab is an 8 inch thick concrete slab with fc of 3,000 psi and grade 40 bars. Typical reinforcing is #5 at 12 inches each way top and bottom. The top reinforcing at typical column strips is increased to 8-#7 instead of 5-#7. Additional bottom reinforcement is added at certain locations. Building Columns: Typical building columns are 18 inches by 18 inches with 4-#8 vertical reinforcement with #3 ties at 16 inch spacing. Column Foundations: Isolated column spread footings vary from 4 feet square to 8 feet square with bottom reinforcing of 4-#4 each way to 11-#5 each way, respectively. Evaluation Results: Ground Floor Slab Over Basement: Most of the ground floor slab over the basement level can support the current code required library loading. The areas where the slab is deficient are the five zones of negative moment at the interior-most columns (note that no additional top steel has been added in these areas; whereas top steel has been added to these areas at the at the other column locations). Deflection and punching shear calculations indicate that deflection and punching shear are not of concern at the ground floor level over the basement. Mezzanine Floor: The mezzanine floor was found to be capable of resisting the current library floor loading, with the exception of the cantilever floor areas at the perimeter of the mezzanine. At the maximum library floor loading upon the cantilevers, the punching shear at the columns supporting the cantilevers is not acceptable. There is also some concern for long Page 16 of 31

17 term deflection at the ends of the cantilever floor areas, where the calculated deflection is approximately 20% larger than acceptable per the code. It appears that the cantilevers can only resist a live load of approximately 80 psf. Columns: Our analysis included the capacity of a typical column that is most heavily loaded under gravity and maximum library floor loading, and we found that the capacity is adequate. Foundations: We checked what appeared to be the most heavily loaded column foundation for gravity and library live loading and found that the soil bearing is approximately 4,000 psf. We do not have the original or current geotechnical report for the building, so we cannot determine whether this bearing pressure is acceptable. We note, however, that the soils are probably very sound because there is no evidence of cracking or settlement in this relatively heavy building. A geotechnical evaluation is necessary to determine the acceptability of library loading impacts on the foundations. VII. SITE OBSERVATIONS: IDS visited the site on April 29, 2011 and performed a visual observation of the readily accessible areas of the building. The site investigation included a visual tour of the exterior of the building, the building roof, and a visual survey at the interior of the building. No testing or destructive investigation was conducted during these visits. It appears that the building was generally constructed in conformance with the available drawings. It also appeared to be in good condition. Photos 1 through 12 on the following pages depict typical observations made during the site visit. Page 17 of 31

18 Site Observation Photos Photo 1: West Side Photo #2: North Side Looking East Photo #3: Northeast Corner, Looking East Photo #4: Southeast Corner, Looking North Page 18 of 31

19 Site Observation Photos (continued) Photo #5: South Side Photo #6: High Roof Over Central Core Photo #7: Typical Precast Sunscreen Panels Photo #8: Interior Central Core Page 19 of 31

20 Site Observation Photos (continued) Photo #9: Interior Showing Conc. Roof Photo #10: Interior Existing Mezzanine Photo #11: Central Core Looking at High Roof Photo #12: Central Core Columns Page 20 of 31

21 VIII. FINDINGS AND RECOMMENDATIONS Possible Retrofit Concepts for Seismic Performance: The key to bringing the Hilb building into compliance with DSA s Enhanced Life Safety performance category along with the building renovation is to address the key areas of concern described above. Briefly, corrective retrofit concepts for each area of concern for seismic performance are described below. These concepts are conceptual only at this time for approximate cost projection purposes only and can be developed into schematic designs for more reliable cost estimating in a future project phase: Strengthen High Roof Columns - Strengthen columns above the main roof level to resist seismic forces from the high roof diaphragm. Install Braced Frames at Building Corners - Add steel braced frames in each direction at the building corners in order to resist seismic forces at the roof level and transfer them directly to the ground. Strengthen Main Roof Diaphragm Strengthen diaphragm connections between the precast concrete panel elements at the main roof to allow the roof to better transfer forces to the perimeter elements. Install Main Roof Chords and Collectors - Add chords and collectors along the perimeter of the main roof in order to transfer forces from the main roof into the corner frames. Possible Retrofit Concepts For Library Loading: In order to strengthen the structure elements found deficient for library conversion as described above, we recommend the following possible retrofit schemes. This work is for the gravity load carrying aspects only; additional retrofits proposed for bringing the building into compliance with DSA s Enhanced Life Safety seismic performance requirements are described in later paragraphs. Ground Floor Slab Over Basement - Since the slab is adequate for deflection and punching shear, only strengthening of the top reinforcing layer is required in selected areas. One common method for this type of strengthening is to apply a fiber reinforced polymer product to the top of the slab in sufficient layers to satisfy the strength requirements. Typical solutions involve either carbon fiber (CFRP) or glass fiber (GFRP) mats impregnated with the polymer material. This would involve removal of all flooring materials and preparing the slab by deep cleaning and/or light sand blasting before the application of the CFRP or GFRP mats. Figure 4 indicates the areas where the fiber reinforced polymer must be installed in order to satisfy code requirements for library floor loading. Mezzanine Floor - Solutions for excessive punching shear stress and cantilever deflection can vary significantly. We judge that the most cost-effective solution would be to install new column drop caps below the floor slab at each column. Added drop caps would entail installing an 8 inch thick by 6 foot square area of thickened concrete at the bottom of the slab, surrounding the column symmetrically. This work would include sand blasting the underside of the existing slab, installing drilled and epoxy-grouted reinforcing, then pumping concrete into formwork or applying shotcrete to create the drop cap. Figure 5 indicates where the new Page 21 of 31

22 column drop caps must be installed if the mezzanine cantilever floor areas are to be used to support library stack loading. Figure 4 Strengthen Ground Floor for Library Loading Page 22 of 31

23 Figure 5 Strengthen Mezzanine for Library Loading Page 23 of 31

24 Opinion of Probable Cost: Our opinion of the probable cost to implement the recommendations indicated in this report is $1,830,000. The seismic retrofit portion of this cost is $1,559,000, and the library upgrade portion is $271,000. Refer to the table below which briefly summarizes the key elements of this value. Our opinion of probable cost at this time is based merely on experience and judgment, and should be more defined as more information is obtained in future studies. The opinion of probable cost covers structural upgrade only, with the assumption that the building will be closed during construction, thus allowing for uninhibited access to perform the structural work. Additional costs for related architectural modifications, ADA compliance, fire and life safety improvements and access modifications are not included in this opinion of probable cost. Page 24 of 31

25 Table of Probable Cost Values Seismic Strengthening Plus Library Floor Strengthening Component Cost 1. Strengthen high roof columns $150, Add steel frames to brace the roof structure $560, Strengthen roof diaphragm connections $220, Add chords and collectors at the roof level $160,000 Subtotal for Seismic $1,090, Strengthen ground floor slab with fiber reinforced polymer $ 50, Add 8 inch thick column drop caps at cantilevers $140,000 Subtotal for Library $ 190,000 Cumulative Subtotal Seismic plus Library Strengthening $1,280,000 General conditions plus Contractor OH & 15% $192,000 Design 15% $192,000 Bonds and 3% $38,000 Contractor Overhead & 10% $128,000 Grand total $1,830,000 (Note: Seismic retrofit portion is $1,559,000, and library upgrade is $271,000) Page 25 of 31

26 Appendix A ASCE 31 Tier 1 Checklists The following checklists were prepared in order to obtain a general understanding as to the types of deficiencies that may be observed from drawing reviews and site observations for the category of structure that best describes the Hilb Center. Each of the evaluation statements on the following checklists shall be marked compliant (C), noncompliant (NC), or not applicable (N/A) for a Tier 1 Evaluation. Compliant statements identify issues that are acceptable according to the criteria of this standard, while non-compliant statements identify issues that require further investigation. Certain statements may not apply to the buildings being evaluated. For non-compliant evaluation statements, the design professional may choose to conduct further investigation using the corresponding Tier 2 evaluation procedure; corresponding section numbers are in parentheses following each evaluation statement. ASCE 31 Geologic Site Hazards and Foundations Checklist C NC N/A COMMENT GEOLOGIC SITE HAZARDS The following statements shall be completed for buildings in levels of high or moderate seismicity. LIQUEFACTION: Liquefaction susceptible, saturated, loose granular soils that could jeopardize the building s seismic performance shall not exist in the foundation soils at depths within 50 feet under the building for Life Safety and Immediate Occupancy. (Tier 2: Sec ) SLOPE FAILURE: The building site shall be sufficiently remote from potential earthquake-induced slope failures or rockfalls to be unaffected by such failures or shall be capable of accommodating any predicted movements without failure. (Tier 2: Sec ) SURFACE FAULT RUPTURE: Surface fault rupture and surface displacement at the building site is not anticipated. (Tier 2: Sec ) CONDITION OF FOUNDATIONS The following statement shall be completed for all Tier 1 building evaluations. FOUNDATION PERFORMANCE: There shall be no evidence of excessive foundation movement such as settlement or heave that would affect the integrity or strength of the structure. (Tier 2: Sec ) Page 26 of 31

27 GEOLOGIC SITE HAZARDS (CONTINUED) The following statement shall be completed for buildings in levels of high or moderate seismicity being evaluated to the Immediate Occupancy Performance Level. DETERIORATION: There shall not be evidence that foundation elements have deteriorated due to corrosion, sulfate attack, material breakdown, or other reasons in a manner that would affect the integrity or strength of the structure. (Tier 2: Sec ) CAPACITY OF FOUNDATIONS The following statement shall be completed for all Tier 1 building evaluations. POLE FOUNDATIONS: Pole foundations shall have a minimum embedment depth of 4 ft. for Life Safety and Immediate Occupancy. (Tier 2: Sec ) C NC N/A COMMENT The following statements shall be completed for buildings in levels of moderate seismicity being evaluated to the Immediate Occupancy Performance Level and for buildings in levels of high seismicity. OVERTURNING: The ratio of the effective horizontal dimension of the lateral-force-resisting system at the foundation level to the building height (base/height) shall be greater than 0.6Sa. (Tier 2: Sec ) TIES BETWEEN FOUNDATION ELEMENTS: The foundation shall have ties adequate to resist seismic forces where footings, piles, and piers are not restrained by beams, slabs, or soils classified as Class A, B, or C. (Tier 2: Sec ) DEEP FOUNDATIONS: Piles and piers shall be capable of transferring the lateral forces between the structure and the soil. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) SLOPING SITES: The difference in foundation embedment depth from one side of the building to another shall not exceed one story in height. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) Page 27 of 31

28 ASCE 31 Basic Structural Checklist for Building Type C2: Concrete Shear Wall Buildings with Rigid or Stiff Diaphragms C3.7.9 Basic Structural Checklist for Building Type C2 These buildings have floor and roof framing that consists of cast-in-place concrete slabs, concrete beams, oneway joists, two-way waffle joists, or flat slabs. Floors are supported on concrete columns or bearing walls. Lateral forces are resisted by cast-in-place concrete shear walls. In older construction, shear walls are lightly reinforced, but often extend throughout the building. In more recent construction, shear walls occur in isolated locations and are more heavily reinforced with boundary elements and closely spaced ties to provide ductile performance. The diaphragms consist of concrete slabs and are stiff relative to the walls. Foundations consist of concrete spread footings or deep pile foundations, or deep foundations. C NC N/A COMMENT BUILDING SYSTEM LOAD PATH: The structure shall contain a minimum of one complete load path for Life Safety and Immediate Occupancy for seismic force effects from any horizontal direction that serves to transfer the inertial forces from the mass to the foundation. (Tier 2: Sec ). MEZZANINES: Interior mezzanine levels shall be braced independently from the main structure, or shall be anchored to the lateral-force-resisting elements of the main structure. (Tier 2: Sec ) WEAK STORY: The strength of the lateral-force-resisting system in any story shall not be less than 80% of the strength in an adjacent story, above or below, for Life- Safety and Immediate Occupancy. (Tier 2: Sec ) SOFT STORY: The stiffness of the lateral-force-resisting system in any story shall not be less than 70% of the lateralforce-resisting system stiffness in an adjacent story above or below, or less than 80% of the average lateral-forceresisting system stiffness off the three stories above or below for Life Safety and Immediate Occupancy. (Tier 2: Sec ) GEOMETRY: There shall be no changes in horizontal dimension of the lateral-force-resisting system of more than 30% in a story relative to adjacent stories for Life Safety and Immediate Occupancy, excluding one-story penthouses and mezzanines. (Tier 2: Sec ) Perform Tier 2 analysis Perform Tier 2 analysis Perform Tier 2 analysis VERTICAL DISCONTINUITIES: All vertical elements in the lateral-force-resisting system shall be continuous to the foundation. (Tier 2: Sec ) Page 28 of 31

29 C NC N/A COMMENT MASS: There shall be no change in effective mass more than 50% from one story to the next for Life Safety and Immediate Occupancy. Light roofs, penthouses and mezzanines need not be considered. (Tier 2: Sec ) TORSION: The estimated distance between the story center of mass and the story center of rigidity shall be less than 20% of the building width in either plan dimension for Life Safety and Immediate Occupancy. (Tier 2: Sec ) DETERIORATION OF CONCRETE: There shall be no visible deterioration of concrete or reinforcing steel in any of the vertical- or lateral-force-resisting elements. (Tier 2: Sec ) POST-TENSIONING ANCHORS: There shall be no evidence of corrosion or spalling in the vicinity of posttensioning or end fittings. Coil anchors shall not have been used. (Tier 2: Sec ) CONCRETE WALL CRACKS: All existing diagonal cracks in wall elements shall be less than 1/8" for Life Safety and 1/16" for Immediate Occupancy, shall not be concentrated in one location, and shall not form an X pattern. (Tier 2: Sec ) LATERAL FORCE RESISTING SYSTEM COMPLETE FRAMES: Steel or concrete frames classified as secondary components shall form a complete vertical load carrying system. (Tier 2: Sec ) REDUNDANCY: The number of lines of shear walls in each principal direction shall be greater than or equal to 2 for Life Safety and Immediate Occupancy. (Tier 2: Sec ) SHEAR STRESS CHECK: The shear stress in the concrete shear walls, calculated using the Quick Check procedure of Section , shall be less than the greater of 100 psi or 2 f' c for Life Safety and Immediate Occupancy. (Tier 2: Sec ) Perform Tier 2 analysis Perform Tier 2 analysis REINFORCING STEEL: The ratio of reinforcing steel area to gross concrete area shall be not less than in the vertical direction and in the horizontal direction for Life Safety and Immediate Occupancy. The spacing of reinforcing steel shall be equal to or less than 18 for Life Safety and Immediate Occupancy. (Tier 2: Sec ) Page 29 of 31

30 C NC N/A COMMENT CONNECTIONS TRANSFER TO SHEAR WALLS: Diaphragms shall be connected for transfer of loads to the shear walls for Life Safety and the connections shall be able to develop the lesser of the shear strength of the walls or diaphragms for Immediate Occupancy. (Tier 2: Sec ) FOUNDATION DOWELS: Wall reinforcement shall be doweled into the foundation for Life Safety and the dowels shall be able to develop the lesser of the strength of the walls or the uplift capacity of the foundation for Immediate Occupancy. (Tier 2: Sec ) ASCE 31 Supplemental Structural Checklist for Building Type C2 Concrete Shear Walls with Stiff Diaphragms C NC N/A COMMENT LATERAL FORCE RESISTING SYSTEM DEFLECTION COMPATIBILITY: Secondary components shall have the shear capacity to develop the flexural strength of the components for Life Safety and shall meet the requirements of , , , , and for Immediate Occupancy. (Tier 2: Sec ) FLAT SLABS: Flat slabs/plates not part of lateral-forceresisting system shall have continuous bottom steel through the column joints for Life Safety and Immediate Occupancy. (Tier 2: Sec ) COUPLING BEAMS: The stirrups in coupling beams over means of egress shall be spaced at or less than d/2 and shall be anchored into the confined core of the beam with hooks of 135º or more for Life Safety. All coupling beams shall comply with the requirements above and shall have the capacity in shear to develop the uplift capacity of the adjacent wall for Immediate Occupancy. (Tier 2: Sec ) OVERTURNING: All shear walls shall have aspect ratios less than 4 to 1. Wall piers need not be considered. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) CONFINEMENT REINFORCING: For shear walls with aspect ratios greater than 2 to 1, the boundary elements shall be confined with spirals or ties with spacing less than 8d b. This statement shall apply to the Immediate Page 30 of 31

31 C NC N/A COMMENT Occupancy Performance Level only. (Tier 2: Sec ) REINFORCING AT OPENINGS: There shall be added trim reinforcement around all wall openings with a dimension greater than three times the thickness of the wall. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) WALL THICKNESS: Thickness of bearing walls shall not be less than 1/25 the unsupported height or length, whichever is shorter, nor less than 4. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) DIAPHRAGMS DIAPHRAGM CONTINUITY: The diaphragm shall not be composed of split-level floors and shall not have expansion joints. (Tier 2: Sec ) OPENINGS AT SHEAR WALLS: Diaphragm openings immediately adjacent to the shear walls shall be less than 25% of the wall length for Life Safety and 15% of the wall length for Immediate Occupancy. (Tier 2: Sec ) PLAN IRREGULARITIES: There shall be tensile capacity to develop the strength of the diaphragm at re-entrant corners or other locations of plan irregularities. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) DIAPHRAGM REINFORCEMENT AT OPENINGS: There shall be reinforcing around all diaphragm openings larger than 50% of the building width in either major plan dimension. This statement shall apply to the Immediate Occupancy Performance Level only. (Tier 2: Sec ) CONNECTIONS UPLIFT AT PILE CAPS: Pile caps shall have top reinforcement and piles shall be anchored to the pile caps for Life Safety, and the pile cap reinforcement and pile anchorage shall be able to develop the tensile capacity of the piles for Immediate Occupancy. (Tier 2: Sec ) Page 31 of 31