B LAST DESIGN INFORMATION FOR

Transcription

1 B LAST DESIGN INFORMATION FOR THE HEFNER VAMC MENTAL HEALTH INPATIENT FACILITY Final Report PEC Report No Prepared for: HDR 400 South Church Street Charlotte, NC Prepared by: Charles J. Oswald, P.E., Ph.D. Marlon Bazan, Ph.D. Protection Engineering Consultants June 9, 2010

2 Executive Summary A new Inpatient Facility is being built at the Hefner VAMC Facility. This construction is only for the first floor of the new inpatient facility. Additional floors will be constructed in a follow-on phase of the overall project. All the construction must meet requirements from the Veterans Administration (VA) for a Mission Critical (MC) Facility. This includes a number of design requirements, including requirements for blast resistance. This report focuses on requirements related to blast design for the Inpatient Facility and it contains blast design information for the roof, steel frame, and wall systems for the Inpatient Facility, as well as blast design requirements for windows to be included in the specifications for the window vendor. The Inpatient Facility is single story steel frame building with a metal stud wall system and a roof system that is built as a composite floor deck. The roof system will become the second floor slab during planned future construction. The metal studs laterally support brick/cast stone veneer walls. Separate steel tube and metal stud frames support the blast resistant windows. The roof system consists of a reinforced concrete slab over a metal deck that is partially composite with steel roof beams. The building is designed to meet progressive collapse requirements by the structural engineer, including a perimeter steel frame with a typical W27x84 girder all around at each floor level. Protection Engineering Consultants (PEC) provided blast design information for the wall system, steel framing, and roof members of the Inpatient Facility, as summarized in Table 1 through Table 3, to meet the blast design requirements of a MC facility. These components will resist the lesser of a GP2 blast load or the blast load from a W2 explosion at 50 ft (GP2 and W2 are defined by the VA on a need-to-know basis) with a maximum dynamic deflection of 1/30 of the span length. The connections loads provided in this information are based on the calculated maximum dynamic reactions from the component response to the design blast loads. They should be resisted by connection strengths based on ASD (Allowable Stress Design). PEC also provided specifications for the window vendor to meet the blast design requirements for MC facilities, as shown in Appendix A. Table 1. Blast Design Information for Steel Framing and Typical Wall Studs Component Typical Span Required Size Design Connection Comment Length (ft) Loads 1 (kips) Steel roof framing and roof slab As shown on structural All beam sizes shown on drawings are acceptable See Table 2 Metal Studs with Brick or Concrete Veneer drawings S (Gr. 50) at 16 inch spacing 1.4 per stud Note 1: All connection loads should be resisted with connections designed using ASD (Allowable Stress Design) Note 2: Use same stud design for areas above windows. Note 3: See Table 3 with design information for steel framing that supports blast resistant windows. 2

3 Table 2. Connection Design Loads for Steel Framing Beam Size ASD Design Load (kips) W21 and larger 65 W18 41 W16 30 W14 43 W12 and smaller 25 W27 perimeter girder 90 Table 3. Blast Design Information for Window Framing Opening 1 Member 1 Member Size Design Connection Single, Double, or Triple Small Window 2,3 (Side-by-side windows, each 3-4 wide ) Screened Porch (15 wide x 8.5 high with jambs at 5 spacing) Loads 4 Sill/Head 800T (Ga. 12) Single Track 8.3 Exterior (2x) 800-S (Ga. 12) Double Stud 2.4 Jamb 5 (4x) 800-S (Ga. 12) Interior 2.7 Jamb 5 (2 Double Studs 4 studs total) Jamb HSS 6x6x3/8 14 Header HSS 4x3x3/8 23 (kips) Note 1: All jambs are assumed to span 13.5 ft from concrete above to concrete below. All headers are assumed to span between jambs. See Table 3 for window area between D4 and C4. Note 2: See Figure 1 for definition of interior and exterior jamb locations. All windows are assumed 3-4 wide. Note 3: Jambs have been designed for a window width of 3-4 Note 4: Design connection loads are per stud. All connection loads should be resisted with connections designed using ASD (Allowable Stress Design). Note 5: Boxed jambs (double studs) should be welded along their height with 1/8 stitch welds (L w =2 ) at 2 ft on center at each side. Exterior Jamb Interior Jamb Exterior Jamb Figure 1. Locations of Interior and Exterior Jambs in Multi-Window Configuration 3

4 Table 3. Window Framing Tube Section Locations Between D4 and C4 Type Size 1 Design Connection Loads 3 (kips) Jamb HSS 6x6x3/8 19 Jamb HSS 6x3x1/2 14 Jamb HSS 3x3x3/8 4 Header 2 HSS 4x3x3/8 14 Note 1: See Figure 2 for member location and orientation. All jambs span 13.5 ft to the concrete above and below. All headers span between jambs. Note 2: All headers are oriented with strong bending axis to resist lateral load. Note 3: All connection loads should be resisted with connections designed using ASD (Allowable Stress Design). Note 4: Double tubes (6x3 next to 3x3) should be welded along their height with 3/16 stitch welds (L w =2 ) at 2 ft on center at each side. N Figure 2. Window Framing Tube Section Locations Between D4 and C4 4

5 Table of Contents 1 Introduction Blast Design Methodology Blast Design Information References...12 Appendices Appendix A. Input for Window Specifications Appendix B. Calculations (provided in separate document) 5

6 List of Figures Figure 1. Locations of Interior and Exterior Jambs in Multi-Window Configuration...3 Figure 2. Window Framing Tube Section Locations Between D4 and C4...4 Figure 3. Blast Load...8 Figure 4. Equivalent SDOF System for Beam...9 List of Tables Table 1. Blast Design Information for Steel Framing and Typical Wall Studs...2 Table 2. Connection Design Loads for Steel Framing...3 Table 3. Blast Design Information for Window Framing...3 Table 4. DIF and SIF Factors...9 6

7 1 Introduction A new Inpatient Facility is being built at the Hefner VAMC site. This construction is the first phase in a larger project to build a new in-patient facility and add more floor space to the Inpatient. All the construction must meet requirements from the Veterans Administration (VA) for a Mission Critical (MC) Facility (Department of Veterans Affairs, 2007). This includes design requirements to resist blast loads and progressive collapse, specified minimum distances from the Inpatient Facility to the nearest parking and drop-off locations and access control requirements for the perimeter around the entire Hefner site. The Inpatient Facility is currently a one-story steel frame building with a reinforced concrete and metal deck roof slab and a metal stud wall system. Metal studs laterally support wall areas with brick/cast stone veneer panels. Separate steel framing supports all window openings for blast-resistant windows. The perimeter frame is designed by the structural engineer to meet progressive collapse requirements with a typical W27x84 girder all around. The current roof system will become a floor system in a successive construction phase for this project. The roof system consists of a reinforced concrete slab over a metal deck that is partially composite with steel roof beams based on the number of steel studs that are provided in the design by the structural engineer. The building has no underground parking area does not have a visitor entry area where any screening will occur. It is attached to a Welcome Center that has a visitor entry area.. This report contains blast design information for the steel framing and metal stud wall system for the Inpatient Facility and blast design requirements for windows to be included in the specifications for the window vendor. The steel roof beams designed by the structural engineer are all adequate to resist the design blast loads and therefore only design reaction loads are provided in this report. The dynamic responses of wall panels and steel framing components to the design blast loads are calculated assuming these components respond as equivalent single-degree-of-freedom (SDOF) systems. 7

8 2 Blast Design Methodology The design blast load for the wall and window systems was based on the lesser of the GP2 blast load or the blast load from a W2 explosion at standoff distance, as required for a MC facility (Department of Veterans Affairs, 2007). The GP2 blast load was used as the design load for wall and window components. The side-on, positive phase blast load was from a W2 explosion at 50 ft was used to check the roof system that was designed by the structural engineer and determine connection design loads to resist reactions from blast. The GP2 blast load was assumed to rise immediately to peak pressure and then decay linearly to ambient pressure over a duration, t d, as shown in Figure 3 The impulse, which is the shaded area under the pressure vs. time curve, is a measure of the total energy in the blast load. The side-on blast load from the W2 explosion was calculated with the SBEDS computer program (PDC-TR 06-01, 2008), which is based on the same methodology as the CONWEP computer program. Pressure Impulse, (i) 0 t d Time Figure 3. Blast Load The structural components were designed to resist their blast load using the SBEDS V4.1 software (SBEDS, 2008), which is distributed by the U.S. Army Corps of Engineers, Protective Design Center (PDC). It models the panels as an equivalent SDOF massspring system with a non-linear spring. This is illustrated in Figure 4. The mass and dynamic load of the equivalent system are based on the panel mass and blast load, respectively, and the spring stiffness and yield load are based on the component flexural stiffness and lateral load flexural capacity. The flexural capacities of the panels include the effects of dynamic increase factors (DIF) applied to the component yield strengths. The minimum static yield strength used for static design is also increased by a static increase factor (SIF). The SIF and DIF are shown in Table 4. These factors are consistent with UFC Design of Structures to Resist Accidental Explosions (2008), as well as numerous other blast design documents. 8

9 Table 4. DIF and SIF Factors Component Type Static Increase Factor (SIF) Dynamic Increase Factor (DIF) Steel studs Hot rolled steel beams Reinforcing steel Concrete Figure 4. Equivalent SDOF System for Beam The properties of the equivalent SDOF system are also based on load and mass transformation factors, which are calculated to cause conservation of energy at each time step between the equivalent SDOF system and the blast-loaded component assuming a constant deformed component shape and that the deflection of the equivalent SDOF system equals the maximum deflection of the component at each time. SBEDS solves the equation of motion for the equivalent SDOF system at each time step using numerical integration and determines the maximum panel dynamic deflection. The maximum deflection from the SBEDS dynamic analyses was divided by the span and compared to a maximum acceptable deflection to span ratio of 1/30, as required for MC facilities. This response level causes damage with some significant deflection, implying the wall and roof members may not be reusable after a design level explosion. The response of reinforced concrete roof deck was limited to a maximum acceptable deflection to span ratio of 1/60, as is typical in other blast design methodologies (UFC , PDC 06-08). Connection forces were calculated based on the reaction forces from the maximum dynamic resistance of the components calculated from the SDOF analyses. For metal studs and tubes supporting windows, the maximum dynamic resistance always equaled the ultimate resistance. For the steel beams, which are subject to a lower side-on blast loading, the maximum dynamic resistance was less than the ultimate dynamic resistance in many cases. This is true because the roof beams are designed by the structural engineer and require a larger size for static and progressive collapse design requirements than for blast design. 9

10 The roof beams were analyzed as partially composite members with the 4.5 inch thick concrete roof deck. The ultimate plastic resisting moment was calculated according to Part 5 of the AISC Manual of Steel Design (AISC, 1995) using material properties that include the SIF and DIF. The amount of compression force in the concrete was typically limited by the number of studs provided by the structural engineer. The moment of inertia was based on the gross moment of inertia of the composite section. These moment capacities and moments of inertias were used in the SBEDS dynamic analyses of the roof beams. The effect of the static self-weight of the roof system was also included. Otherwise, all SDOF properties of roof and wall components were calculated with SBEDS as stated in the SBEDS Methodology Manual (PDC-TR 06-01, 2008). The columns of the Inpatient Facility do not require dynamic design since they are not directly loaded by blast load, all the wall components span from floor-to-floor. Also, the Inpatient Facility is only one story with an approximately square footprint and significant inertia force from the mass at roof level, and therefore does not require any design or analysis for lateral sway from blast load. 10

11 3 Blast Design Information Table 1 through Table 3 in the Executive Summary shows a summary of blast design information for the Inpatient Facility. Information shown in Appendix A is provided as input for the window specifications. This information gives performance criteria for the design of the window glazing, glazing attachment to the frame, frame attachment to the structure, and for mullions supporting the windows. The mullion deflection is limited to 1/30 of the span (3.8 degrees of support rotation), as required for a MC facility. Also, laminated glass is required for single pane glass and for the interior pane of insulated glass units (IGU). HDR should add any requirements related to the energy efficiency of the windows to the specifications. These requirements, which may include use of IGUs, rather than single pane windows, and low emission requirements for the outer pane of the IGU, will not inhibit the blast performance of the window. 11

12 4 References American Society of Civil Engineers, Design of Blast Resistant Buildings for Petrochemical Facilities, New York, NY, American Institute of Steel Construction (AISC), Manual of Steel Construction, Load and Resistance Factor Design (LRFD), Chicago, IL, Department of Veterans Affairs, Physical Security Design Manual for VA Facilities Mission Critical Facilities, Washington, DC, July PDC-TR Rev1, Methodology Manual for the Single-Degree-of- Freedom Blast Effects Design Spreadsheets (SBEDS), U.S. Army Corps of Engineers, Protective Design Center (PDC) Technical Report, PDC-TR Rev 1, Single Degree of Freedom Structural Response Limits for Antiterrorism Design, U.S. Army Corps of Engineers, Protective Design Center (PDC) Technical Report, UFC , "Structures to Resist the Effects of Accidental Explosions," Department of Defense, Washington, DC, SBEDS (Single degree of freedom Blast Effects Design Spreadsheet), Version 4.1, US Army Corps of Engineers Omaha District, Protective Design Center, Omaha, Nebraska, August,

13 Appendix A Addition to Window Specifications for Blast Design

14 Blast Resistance: All glazing shall be designed using WinGARD V3.15 or later software or HazL V1.2 to achieve a glass performance condition 3b (i.e., glazing fails but fragments land on floor no further than 3 m (10 ft.) from the vertical plane of the window). The analysis shall account for the height of the bottom of the glazing to the floor in determining the performance condition. The glazing shall be designed for a GP2 blast load (Note: actual blast load information is provided in separate document sent to HDR). All glazing shall consist of laminated glass for single pane constructions or laminated glass for the inboard (non-threat side) pane of an insulating glass unit (IGU) constructions. All glazing shall be adhered to its supporting frame using structural silicone sealant or adhesive glazing tape. The width of the structural silicone sealant bead shall be at least equal to the larger of 10-mm (3 8-in.) or the thickness designation of the glass to which it adheres, but not larger than two times the thickness designation of the glass to which it adheres. The minimum thickness of the structural silicone bead shall be 5-mm (3 16- in.). The width of glazing tape shall be at least equal to two times but not more than four times the thickness designation of the glass to which it adheres. The structural silicone bead or glazing tape shall be applied to both sides of single pane laminated glass constructions, but need only be applied to the inboard side (non-threat side) of IGU constructions. The frames and mullions for all blast resistant glazing shall transfer the dynamic reaction loads from the glazing into the supporting structure as follows. Connections of frames directly to the structure (i.e. steel tubes) shall have a nominal design capacity that resists an equivalent static load equal to the reaction loads from the peak resistance of the window (R max ), as determined from WinGARD or HazL, uniformly distributed around the perimeter of the glazing. Mullions shall be designed to resist either the calculated dynamic reactions from the glazing response or the design blast load over the tributary area using dynamic analysis, with a maximum deflection of L/30 where L is the mullion span length. The connections of mullions shall be designed to resist reaction forces based on the ultimate flexural resistance of the mullion or the peak dynamic reaction force determined in the dynamic analysis.