Pennsylvania Judicial Center Prevention of Progressive Collapse Resulting

Pennsylvania Judicial Center: Prevention of Progressive Collapse Resulting from an Interior Blast Loading Brian M. Barna Structural Option AE Senior Thesis – Spring 2007

Introduction of Topics n n n n Defining the design blast load Composite column design Mitigation of progressive collapse Blast design for glazing Cost impact of blast design Mechanical changes Architectural changes

Building Background n n n n Nine stories 425, 000 sq. ft Harrisburg, PA $90 -95 million Construction from Fall 2006 – Fall 2008 Center of Unified Judicial System Courtrooms and offices

Building Background n n n Owner: Pa. State Government A/E Firm: Vitetta Construction: Heery International

Structural Features n Composite steel frame W 16 x 36 to W 24 x 68 typical n Spans < 42’, Spacing 10’ typical n LW Concrete, f’c = 4000 psi n n n Concentrically braced frames (R=3. 25) Foundation made of piers and caissons

Architectural Features n n n Indiana limestone to match surrounding buildings Modern and conservative Five story atrium 3 rectangular forms Future expansion

Typical Floor Plan

Selection of Design Blast Location n n Bordered on three faces Gathering space and highway in front High level of security Lower level parking garage

Parking Garage Plan

Selection of Design Blast Force n n n Define load as a max loaded car bomb 1000 lbs TNT Equivalency

Selection of Design Blast Force n n 25’ standoff distance Scaled distance ‘Z’ (TM 5 -1300): Pso = 200 psi = 28. 8 kips/sq. ft. Positive impulse lasts for milliseconds

Charge Pressure-Time Chart

Composite Columns n n n Existing concrete Protection of the steel column Static analysis Max of 1 column incapacitated Direct shear capacity

Composite Columns Shape no steel Min. dim. 39 x 39 W 12 x 170 36 x 36 W 12 x 210 35 x 35 W 12 x 230 35 x 35 W 14 x 257 33 x 33 W 14 x 311 31 x 31 W 14 x 500 23 x 23

AISC Blast Test n n 4000 lbs @ 12’ Pso = 1500 psi W 14 x 233 Brick cladding

AISC Blast Test n n n dx = 4” dy = 1. 5” Still usable for prog collapse mitigation Damage

Vierendeel Trusses n n Moment frames Improve redundancy Allow redistribution of load Progressive collapse only n Adequate wind/seimic FRS already exists

Vierendeel Trusses n n n Strength, life safety only concerns Serviceability, deflection not considered GSA: 0. 82 D + 0. 2 L is conservative n n Includes Wo (1. 1) and f (0. 9) My design: 1. 0 D + 0. 25 L n No reliance on overstrength

Vierendeel Trusses Stress Diagram – 0. 82 D + 0. 2 L

Vierendeel Trusses Final Design

Blast-resistant Glazing n n Glass shards represent serious hazard in blast scenario Blasts capable of projecting shards at speeds >70 MPH 40% of Ok. City bombing injuries 5, 000 injured by glass and debris in 1998 U. S. Embassy bombing in Kenya

ASTM E 1300 n Strength determined by: Glass type n Window dimensions n Glazing thickness n n For 3 sec loading (conservative for blast)

ASTM E 1300 n n n Limited to 10. 0 k. Pa Most windows fail due to short standoff distance Therefore, changing dimensions, thickness not the best way to improve blast resistance

Laminated glass n Keeps glazing in pocket Protects life safety Does not prevent breakage n Other option: ASF n n Usually retrofit n More expensive n

Cost of new systems n Vierendeel Trusses Larger members +$62, 000 n Moment connx. + $3, 600 n n Composite Columns n n Blast-resistant glazing n n Add’l cost is neglegible Laminated IGU’s +$27, 400 +$93, 000 0. 1% increase for $95 million building cost

Mechanical system n n n Combat bioterrorism attack Automatically flush contaminants from air Design for two 3 rd floor courtrooms 6 AC/hour (7560 cfm) Negative pressure in room n Vsupply < Vexhaust

Mechanical System n n Normal Supply Condition: 2930 cfm Contamination Condition: 5690 cfm Controlled by supply fan modules n 4. 5 AC/hour n n Upgrade AHU to Mc. Quay Vision CAH 008 Min supply: 2200 cfm n Max supply: 6000 cfm n n Exhaust Fan: Penn. Barry Fumex FX 18 V n (3) fans per room @ 3023 cfm = 9069 cfm

Mechanical System n n n 12”x 16” rectangular ducts Separate duct run for each exhaust Final exhaust must be 10 m from occupancy Plume center (C=Co) 10 m Exhaust Stack 20 m Plume extent where C = 0. 02 Co

Mechanical System n Cost of new system Larger A. H. U. n Exhaust fans n Ductwork n n + $6, 000 + $9, 600 +$23, 500 +$39, 100 This cost does not include structure, cladding of stacks

Before

After

Conclusions and Recommendations n All blast-resistant designs implemented n n Benefit vs. Cost New mechanical system not used Limited use n Security n n n Better design aids and procedures needed More research needed for blast design

Questions?