Appendix_BB_-_Seismic_Eval_of_Exisit_Building_97_Struct.pdf

PRELIMINARY SEISMIC EVALUATION

OF AIRMENS DORMITORY-

BUILDING #97

Thule Air Base, Greenland

Prepared for:

US Army Corps of Engineers, NY District 26 Federal Plaza, New York, NY 10278

Prepared by:

Jacobs/ Ammann & Whitney JV

May 30, 2014

USACE- NY District: Thule Air Base, Greenland 05/30/2014 Airmens Dormitory- Building #97

Preliminary Seismic Evaluation of Existing Building

TABLE OF CONTENTS

1. EXECUTIVE SUMMARY 1

2. SCOPE OF WORK 2

3. SEISMIC PERFORMANCE/ EVALUATION CRITERIA 3

4. EXISTING BUILDING STRUCTURE 5

5. STRUCTURAL EVALUATION 14

6. SUMMARY & CONCLUSIONS 16

APPENDIX A: STRUCTURAL CALCULATIONS A-1

APPENDIX B: REFERENCES B-1

Preliminary Seismic Evaluation of Existing Building 2

1. EXECUTIVE SUMMARY

The current efforts involved an engineering-level Preliminary Seismic Evaluation of the existing Airmens Dormitory building #97 at Thule Air Base, Greenland. As per the direction of USACE-NY, Jacobs/ Ammann & Whitney JV engineers investigated the adequacy and feasibility of retrofitting the existing building structure to meet the targeted performance requirements and to withstand the increased seismic loading demands. Our scope of work included determination of code-required structural loading, modeling of the existing building structural framing, performing preliminary structural analyses considering various load combinations that involve seismic effects and evaluating the need for and the feasibility of structural retrofitting.

Provisions of UFC 3-301-012, UFC 3-310-043, IBC-124, and ASCE 7-105 were implemented to identify the applicable seismic hazards and analytical procedures to evaluate the structural adequacy of the existing building. Specifics of the existing building were obtained from the As-Built drawings1 provided by USACE-NY and RISA-3D8 software was utilized to perform structural analyses of the investigated building and Provisions of AISC-SCM7 were applied to compute structural strengths of various framing components.

The following conclusions can be deducted based on our preliminary investigation:

The proposed addition to the existing dormitory building will trigger a requirement of upgrading the strength of the existing building to withstand increased seismic loading effects.

As per applicable UFCs and building codes’ requirements, the target building performance level is “Life Safety” for both structural and non-structural components.

Building site classification has a considerable influence on the seismic demand (i.e. design category, loading and detailing) therefore, it is recommended to perform a site-specific investigation to determine the site soil class.

The expected structural retrofit efforts would involve strengthening of the building primary structural framing (i.e. floor beams and beam-column connections). It is unlikely that there would be any need to strengthen the existing building foundation system.

In conclusion, based on our preliminary analyses and considering the estimated seismic loading demands, we concluded that it is practically feasible to retrofit the existing dormitory building structure to meet the additional strength demands required by applicable building codes.

Preliminary Seismic Evaluation of Existing Building 3

2. SCOPE OF WORK

Task 1: Review Available Design Documents

This initial task is necessary to extract important information required for performing the seismic evaluation of the existing building using available As-Built Drawings1 and documents.

Task 2: Identify Applicable Seismic Performance Criteria

This task identifies the performance objectives to be utilized in the evaluation of the existing building and in deciding on the need for and level of structural retrofit. These performance objectives are obtained from UFC 3-310-043 and are applied as per the guidance of ASCE/SEI 41-136.

Task 3: Estimate Applicable Structural Loads

This task compiles estimates of structural load effects (i.e. dead, live, snow, wind, and seismic) considered in the evaluation of the building structure. Load information were obtained from available as-built drawings and computed as per the provisions of applicable building codes/ standards (i.e. UFC 3- 301-012, UFC 3-310-043, IBC-124, and ASCE 7-105).

Task 4: Develop a Structural Model of the Investigated Building

This task involves utilizing RISA-3D8 software to model various components of the primary structural framing of a representative portion of the investigated building. The model will represent the building geometry, materials, member sizing, connection types, applied loading, and support conditions.

Task 5: Compute Strength Demands for Various Load Combinations

This task involves the utilization of the previously constructed RISA-3D model to estimate internal forces due to various individual load cases and to compute the strength demands for various members (i.e.

columns, beams, connections, foundations) as per applicable code-defined load combinations.

Task 6: Evaluate the Need and Feasibility of Retrofitting the Existing Building

This task provides an assessment of structural adequacy of the investigated existing building to withstand the updated combined load effects as per current code requirements including increased seismic demands.

Available structural strengths of various components of the existing building are computed using the information and code requirements included in AISC-SCM7. Targeted performance criteria are to be used to evaluate the structure adequacy and will facilitate the identification of areas in need for strengthening.

Task 7: Prepare Seismic Evaluation Report

This final task provides documentation of performed analyses and design calculations. The report includes the following sections: 1-Executive Summary, 2- Scope of Work, 3- Seismic Performance/ Evaluation Criteria, 4- Existing Building Structure, 5- Structural Evaluation, 6-Summary & Conclusions, and Appendices A, B.

Preliminary Seismic Evaluation of Existing Building 4

3. SEISMIC PERFORMANCE/ EVALUATION CRITERIA

3.1 SEISMIC HAZARD LEVELS

ASCE/SEI 41-136, “Seismic Evaluation and Retrofit Rehabilitation of Existing Buildings” provides guidance on seismic hazard levels applicable to evaluation or rehabilitation levels. Table 3.1 below provides ASCE/SEI 41-13 applicable seismic hazard levels for the investigated building at Thule AB.

Table 3.1 Seismic Hazard Levels

Seismic Hazard Level

Applicability Probability of Exceedance

Mean Recurrence Interval (MRI)

BSE-1E Existing 20% in 50-yrs 225

BSE-2E Existing 5% in 50-yrs 975

BSE-1N Existing / New

BSE-2N Existing / New 2% in 50-yrs 2500

3.2 SEISMIC PERFORMANCE OBJECTIVES

ASCE/SEI 41-136, provides guidance on Basic Performance Objectives for Existing Buildings (BPOE).

Table 3.2 below provides ASCE/SEI 41-13 Performance objectives as applicable to the investigated building at Thule AB.

Table 3.2 Seismic Performance Objectives

Tier 1 Tier 2 Tier 3

Risk Category

BSE-1E BSE-1E BSE-1E BSE-2E

I , II

Life Safety Structural

Performance

Life Safety Non- Structural

Performance

(3-C)

Life Safety Structural

Performance

Life Safety Non- Structural

Performance

(3-C)

Life Safety Structural

Performance

Life Safety Non- Structural

Performance

(3-C)

Collapse Prevention Structural

Performance

Non-Structural Performance not

Considered

(5-D)

UFC 3-310-043 “Seismic Design of Buildings” Section 2-3401.8 “Performance Objectives for Evaluation and Retrofit using ASCE/SEI 41-13” provides guidance on applicable objectives for buildings according to Risk Category (i.e. I, II, III, IV), Scope Item (i.e. Structural or Non-Structural) and type of applications (i.e. Evaluation or Retrofit). Table 3.3 below provides UFC 3-310-04 applicable performance objectives for the investigated building at Thule AB.

Table 3.3 Seismic Performance Objectives

Risk Category

Scope Item Evaluation Performance Objectives

Retrofit Performance Objectives

I , II

Structural Life Safety in BSE-1E Life Safety in BSE-1N

Collapse Prevention in BSE-2N

Non-Structural Life Safety in BSE-1E Life Safety in BSE-1N

Preliminary Seismic Evaluation of Existing Building 5

3.3 SEISMIC GROUND MOTION PARAMETERS

UFC 3-301-012 “Structural Engineering” Section 2-1.6 “Section 1613 - EARTHQUAKE LOADS” references Table F-3 “EARTHQUAKE LOADING DATA” of the UFC document to identify applicable seismic ground motion parameters. Table 3.4 below provides UFC 3-301-01 applicable seismic parameters for the investigated building site at Thule AB.

Table 3.4 Seismic Ground Motion Parameters

Seismic Data (Site Class B)

Base/ City Ss

(% g)

S1

(% g)

Ss 10/50

(% g)

S1 10/50

(% g)

Thule AB 39.0 18.0 20.0 9.0

4. EXISITNG BUILDING STRUCTURE

4.1 BUILDING CONFIGURATIONS

The existing dormitory building #97 is a multi-story steel frame building designed and built at Thule air Base, Greenland in 1960’s. As can be seen from figure 4.1, the building has a rectangular foot print with an overall length of 227-ft and width of 40-ft. The building layout is modular with uniform column grid spaced at 12.5-ft in the East-West direction and 16/6/16-ft in the North-South direction. Figure 4.2 provides an elevation of the building and shows the structure to be composed of three typical floors, one framed ceiling and a gabled roof accounting for a full eave height of 32-ft above grade level. Figure 4.3 provides a vertical section though the building in the building main framing direction. This figure also shows that the building 1st floor slab is elevated above grade level by 4.67 ft to avoid unwanted effects of supporting 1st floor slab on a perma-frost grade.

4.2 BUILDING STRUCTURAL SYSTEM

4.2.1 Foundation System

Figure 4.4 shows the building foundation system to be composed of isolated/ combined footings under steel columns which are connected by grid beams in both building directions. As per the information in “foundation plan and details” drawing, all footings were constructed using 3000 psi concrete and sized based on an allowable soil bearing capacity of 4000 psf.

4.2.2 Gravity Load Carrying System

4.2.2.1 1st, 2nd, 3rd Floors Figures 4.5, 4.6 show the building’s typical floor system to be composed of 2-in concrete topping over 4.4-in cellular metal floor deck spanning 12.5-ft in the East-West direction between floor beams. Primary floor A-36 steel beams (12WF31, 27, 19) support floor slab and span 15.67-ft in the North-South direction between steel columns. Secondary floor A-36 steel beams (8C11.5) support exterior walls and span 12.5-ft in the East-West direction between floor end brackets. Secondary floor A-36 steel beams (8B10, 6B8.5) support interior walls and span 12.5-ft in the East-West direction between steel columns.

Preliminary Seismic Evaluation of Existing Building 6

4.2.2.2 3rd Floor Ceiling The ceiling system is composed of 1.5-in cellular metal floor deck spanning 12.5-ft in the East-West direction between floor beams. Primary A-36 steel beams (12B16.5) support floor deck and span 15.67-ft in the North-South direction between steel columns. Secondary A-36 steel beams (8C11.5) support exterior walls and span 12.5-ft in the East-West direction between end brackets. Secondary A-36 steel beams (6B8.5) span 12.5-ft in the East-West direction between steel columns.

4.2.2.3 Roof

Figure 4.7 shows the building’s roof system to be composed of a 1.5-in metal roof deck spanning 6-ft in the North-South direction between roof purlins. A-36 steel roof purlins (6B8.5) support roof deck and span 12.5-ft in the East-West direction between primary roof beams. A-36 roof beams (8B13) support roof purlins and span 15.67-ft in the North-South direction between steel columns.

4.2.2.4 Columns

Exterior A-36 steel columns (8WF31) and Interior steel columns (8WF40) provide support to floor and roof beams and extend for the full height between the building footings to its roof with their strong directions aligned in the North-South direction.

4.2.3 Lateral Load Carrying System

As can be determined from all available drawings, the investigated building utilizes steel moment resisting frames in both directions to provide structural stability and resistance to applied lateral loads. In the North-South direction, two single-bay moment frames connected by link-beams (17 interior and 2 exterior frames) constitute the lateral-resisting system in the building short direction. In the East-West direction, multi-bay moment frames (2 interior and 2 exterior frames) constitute the lateral-resisting system in the building long direction. All frames are considered as “rigid frames” and their level of detailing suggests a classification of “Ordinary” moment resisting frames. All floors slabs, ceiling and roof decks are considered to serve as “Rigid” diaphragms to transfer applied lateral loads (i.e. seismic, wind) to supporting frames according to their relative stiffness.

4.2.4 Frame Connections

Figure 4.8 shows sample details of typical beam-column framed connections. It can be seen that in the primary frame direction (i.e. North-South), beam-to-column connections are “End-Plate”, “Bolted” moment connections. For analytical purposes, these connections are considered as “Rigid” connections.

As for the secondary frame direction (i.e. East-West), beam-to-column connections are also “End-Plate”, “Bolted” moment connections, however, with much less moment capacity. Even though these connections are relatively flexible and tend to behave as “Semi-Rigid”, it was decided to consider these connections as “Rigid” connections as well to simplify modelling efforts.

Figure 4.9 shows typical details of column-base connections. It can be seen that as per this detailing, column bases do not have sufficient restraint to potential base rotations and therefore, column base support conditions were considered to be “Pinned” for analytical purposes.

Preliminary Seismic Evaluation of Existing Building 7

Figure 4.1 Building 1st Floor Plan

Figure 4.2 Building South Elevation

Preliminary Seismic Evaluation of Existing Building 8

Figure 4.3 Building Vertical Section

Preliminary Seismic Evaluation of Existing Building 9

Figure 4.4 Building Partial Foundation Plan

Preliminary Seismic Evaluation of Existing Building 10

Figure 4.5 Building Partial 2nd / 3rd Floor Deck Plan

Preliminary Seismic Evaluation of Existing Building 11

Figure 4.6 Building Partial 2nd / 3rd Floor Framing Plan

Preliminary Seismic Evaluation of Existing Building 12

Figure 4.7 Building Partial Roof Framing Plan

Preliminary Seismic Evaluation of Existing Building 13

Figure 4.8 Sample Floor Beam-Column Connections

Figure 4.9 Typical Column-Base Connections

Preliminary Seismic Evaluation of Existing Building 14

5. STRUCTURAL EVALUATION

5.1. OBJECTIVE

The purpose of the current structural evaluation is to provide an assessment of the structural adequacy of the existing dormitory building structure. Prior to investing in any building’s additions or rehabilitation efforts, it is essential to gauge the building structural performance as per available as-built information. Designed and built in the 60’s, it is expected that building structural capacities may not be adequate in some aspects to meet current code requirements, especially those related to seismic loading demands. The primary objective of this preliminary investigation is to answer three questions:

1- Can the dormitory building withstand current code loading requirements?

If the answer to the first question is NO, then

2- Is structural retrofitting feasible?

3- What level of structural retrofit would be necessary to bring the building up to conformance to current building codes requirements?

5.2. EVALUATION APPROACH

Based on the limited scope of the current investigation, a limited analytical approach was deemed appropriate to achieve the evaluation objectives. The following sequence of tasks provides the frame-work of the analytical approach:

1- Collect relevant building information necessary to prepare a structural model. As presented in Chapter-4, dormitory building information was obtained from available As-Built drawings.

2- Construct a 3-D structural model of a representative portion of the building. RISA-3D software was utilized to create the mathematical model of the building structure.

3- Identify targeted building performance objectives. As presented in Chapter-3, UFC 3-301-01, UFC 3-310-04 and ASCE 41-13 were considered the primary sources for performance objectives.

4- Compute estimates of various code-required load effects applicable to the investigated building.

This includes dead, live, snow, wind, and seismic loading.

5- Perform structural analyses to determine internal forces developed within various framing elements under the effects of various load cases. Utilize applicable ASCE 7-10 load combinations to compute expected loading demands on primary structural members.

6- Estimate the structural capacities of representative components of the building’s structural framing (i.e. beams, columns, connections) using available As-Built information and applying the provisions of AISC-. SCM.

7- Evaluate the adequacy of the building structure by comparing available structural capacities of representative components to expected loading demands. Identify type, extent, and level of observed structural deficiencies and make a judgment about the feasibility of a structural retrofit.

5.3. STRUCTURAL CALCULATIONS

Appendix-A documents all design calculations and performed analysis details. A-1 Structural Loads includes calculations of various loading effects as per the provisions of ASCE 7-10. A-2 RISA-3D Model provides graphical representation of considered structural framing including geometrical and material characteristics, structural arrangements, loading, and boundary conditions. A-3 Analysis Results presents the outcome of the structural evaluation in terms of loading demands and adequacy checks as per applicable codes.

Preliminary Seismic Evaluation of Existing Building 15

5.4. HIGHLIGHTS OF PERFORMED EVALUATION

5.4.1 3-D Structural Model

a) Due to the modular nature of the building, a partial building model was considered sufficient to provide necessary information for the preliminary-level evaluation.

b) All structural steel members were assumed to be constructed of ASTM A-36.

c) In lieu of accurate section information for steel sections from the 60’s era, equivalent (i.e.

size, weight) rolled steel shapes were assumed for steel beams and columns.

d) Full rigid joints were assumed for all framed moment connections.

e) Due to the uncertainty about the composite action between floor slabs and supporting beams, it was decided to ignore any composite action and assumed floor beams as steel-only beams.

f) Floor slabs and roof decks were assumed as rigid diaphragms transferring lateral loads to supporting moment frames.

5.4.2 Structural Loads

a) Superimposed dead loads and Live loads were estimated based on information obtained from

As-Built drawings.

b) Snow loads were computed using ASCE 7-10 provisions and using UFC 3-301-01 recommendations for ground snow = 25 psf at Thule AB.

c) Wind loads were computed using ASCE 7-10 provisions and using UFC 3-301-01 recommendations for basic wind speed = 171 mph at Thule AB.

d) Earthquake loads were computed using “Life Safety” performance objective for existing buildings as recommended by UFC 3-310-04 and ASCE 41-13.

e) Earthquake loads were computed assuming conservatively that the investigated building is constructed on a “Site Class D” soil.

f) Earthquake loads were computed using ASCE 7-10 provisions and using UFC 3-301-01 recommendations for spectral seismic parameters for evaluation of existing buildings (Ss-10/50 = 0.2 g, S1-10/50 = 0.09 g) at Thule AB.

g) Applicable load combinations including combined gravity and lateral load effects were identified as per the provisions of ASCE 7-10

5.4.2 Building Structural Adequacy

a) Only strength-based adequacy evaluations were considered. Other deformation-based evaluations more applicable to serviceability conditions were deferred to more refined, higher-level future investigations.

b) Structural capacities of representative framing members were computed by built-in modules within RISA-3D. More detailed strength computations were deferred to more refined, higher-level future investigations.

c) Structural capacities of connections were not evaluated at this level of investigation. It was assumed that the existing building connection design was based on its member design (i.e.

adequate member design ≡ adequate connection design). More detailed strength computations were deferred to more refined, higher-level future investigations.

d) Structural adequacy checks were reported in terms of RISA-3d “Stress Unity Checks”. A unity check > 1.0 indicates a deficient component that is graphically highlighted in “Red”.

Preliminary Seismic Evaluation of Existing Building 16

6. SUMMARY & CONCLUSIONS

The current efforts involved an engineering-level Preliminary Seismic Evaluation of the existing Airmens Dormitory building #97 at Thule Air Base, Greenland. Our engineers investigated the feasibility of retrofitting the existing building structure to meet the targeted performance requirements and to withstand the seismic loading demands required by applicable building codes as a result of the proposed additions to the existing building. Our efforts included determination of code-driven seismic loading requirements, modeling of the existing building frames, performing preliminary structural analyses considering various load combinations that involve seismic effects and evaluating the need and feasibility for structural retrofitting.

Provisions of UFC 3-301-01, UFC 3-310-04, ASCE 41-13, and ASCE 7-10 were implemented to identify the applicable seismic hazards and analytical procedures to evaluate the structural adequacy of the existing building. Specifics of the existing building were obtained from the As-Built drawings provided by USACE-NY and RISA-3D software was utilized to perform structural analyses of the investigated building. The following lists our conclusions for the seismic evaluation:

The size and configuration of the proposed addition of a full-height new building area to the existing dormitory building will trigger a requirement of upgrading the strength of the amended building to withstand the most-recent applicable code-driven seismic loading effects.

As per applicable UFCs and building codes’ requirements, it was determined that the target building performance level is “Life Safety” for both structural and non-structural components.

This evaluation/ retrofit performance level is typically associated with moderate damage levels.

As per UFC 3-310-04 and ASCE-41 provisions, the seismic hazard associated with this life safety performance level was determined to be “BSE-1E” associated with 20% probability of exceedance in 50-years with MRI of 225 years.

Our preliminary investigation indicated the importance and influence of the accurate identification of the building site classification on the seismic design category and corresponding seismic loading and detailing demands. If such information is not readily available, we recommend performing a limited site-specific investigation to determine the site soil class prior to engaging in any seismic retrofit design efforts.

As per our evaluation, we concluded that the expected structural retrofit efforts would involve strengthening of the building primary structural framing (i.e. floor beams and beam-column connections). It is unlikely that there would be any need to strengthen the existing building foundation system.

In conclusion, based on our preliminary analyses and considering the estimated seismic loading demands, we concluded that it is practically feasible to retrofit the existing dormitory building structure to meet the additional strength demands required by applicable building codes.

USACE- NY District: Thule Air Base, Greenland 05/31/2014

Preliminary Seismic Evaluation of Existing Building A-1

APPENDIX A:

STRUCTURAL CALCULATIONS:

A-1 Structural Loads A-2 RISA-3D Model A-3 Analysis Results

Preliminary Seismic Evaluation of Existing Building B-1

APPENDIX B:

REFERENCES

Preliminary Seismic Evaluation of Existing Building B-2

1- USACE- Eastern Ocean- NY District, “As Built Drawings for Airmens Dormitory, Thule Air Base”, Thule, Greenland, 1960.

2- UFC 3-301-01, “Structural Engineering”, Unified Facility Criteria, Department of Defense, June 2013.

3- UFC 3-310-04, “Seismic Design of Buildings”, Unified Facility Criteria, Department of Defense, June 2013.

4- IBC-12, “International Building Code”, International Code Council Inc, 2012

5- ASCE/SEI 7-10, “Minimum Design Loads for Buildings and Other Structures”, ASCE Standard, American Society of Civil Engineers, 2010.

6- ASCE/SEI 41-13, “Seismic Evaluation and Retrofit Rehabilitation of Existing Buildings”, ASCE Standard, American Society of Civil Engineers, 2013.

7- AISC SCM-14th Ed, “Steel Construction Manual”, American Institute of Steel Construction, 2011

8- RISA-3D Ver 9.0, “Structural Analysis/ Design Software”, RISA Technologies, 2010