Armed Forces Retirement HomeDesign Build Services Request for Proposal

Gulfport, Mississippi21 May 2007

C – STRUCTURAL

CODES AND STANDARDS

The International Building Code (IBC) is the governing building code to guide the structural design for this project. Current design and construction standards and specifications such as those provided by ACI, AISC, AWS, ASCE, and GSA shall also be used. Only the major codes and standards applicable to this project are referenced in Section N - Building Codes and Standards. Other industry standards and specifications may also be applicable. Tables, figures, and descriptions included in this narrative are based on the latest editions of structural design standards currently available (e.g. IBC-06, ASCE 7-05, ACI 318-05, etc.).

STRUCTURAL LOADS

The site is located in a hurricane prone region that is subject to flooding, wind-borne debris, and high wind gusts. Given the owner’s goal to minimize evacuations and to have residents safely remain onsite to the extent practicable during major storms, the importance factor for this building shall be increased to the requirement of an essential facility for wind load only (IBC Table 1604.5).

LIVE LOADS

Minimum live loads shall be in accordance with IBC Section 1607 and Table 1607.1. Selected portions of Table 1607.1 are reproduced here for reference.

Roof:20-psf

(reduce by tributary area per code)

Balconies:100-psf

Private rooms and corridors serving them:40-psf

Public rooms and corridors serving them:100-psf

Parking Garage:40-psf

Stairs and exits:100-psf

Library:

Corridor80-psf

Reading rooms60-psf

Stack rooms150-psf

Assembly areas:

Fixed seats60-psf

Projection and control room50-psf

Lobbies100-psf

Movable seats100-psf

Stages and platforms125-psf

WIND LOADS

Wind loads shall be determined in accordance with Chapter 6 of ASCE 7. As described in IBC 1609.1.2 and ASCE 6.5.9.3, glazing shall be impact-resistant or protected with an impact-resistant covering meeting the requirements of ASTM E 1996 and ASTM E 1886. In accordance with ASCE 6.5.9.3, glazing located over 60 feet above the ground and over 30feetabove aggregate surface roofs located within 1500feet of the building shall be permitted to be unprotected. Wind analysis shall be based on the following criteria.

Basic Wind Speed (3-sec gust):150-mphASCE Figure 6-1

Importance Factor (Iw):1.15ASCE Table 6-1

Surface Roughness Category:CASCE Section 6.5.6.2

Exposure Category:CASCE Section 6.5.6.3

Appendix C6 of ASCE 7 (commentary) provides a correlation of the mapped basic wind speed and the Saffir/Simpson Scale that is used by the National Hurricane Center for reporting hurricane intensities.Hurricanes are grouped in Categories 1 through 5 with Category 5 being the worst case – see table below. The factored wind speed based on the specifiedprojectdesign criteria is 1.15 x (1.6)0.5 x 150-mph = 218-mph. This value exceeds thespeed of 191-mph that defines the lower Category 5 Hurricane listed in ASCE Table C6-5 by approximately 14%.

Hurricane Category(1) / WindSpeedRange(2)
(mph) / Factored Design Wind Speed for this Project
(mph)
1 / 82 – 108 / -
2 / 109 – 130 / -
3 / 131 – 156 / -
4 / 157 – 191 / -
5 / > 191 / 218

Footnotes:

1) Based on Saffir/Simpson Scale used by the NationalHurricaneCenter.

2) 3-second gust wind speed at 33-ft above open terrain.

FLOOD LOADS

The structure is located in a flood hazard area and consideration of flooding is important. The owner’s goal is to locate mechanical equipment on floors at least 35 feet above sea level to allow free passage of floodwaters without damage to the structure or supporting foundation system. Flood design shall be based on ASCE 24 (Flood Resistant).

Design and Construction using design Category IV (ASCE 24 Table 1-1). Consult local Flood Hazard Maps to determine site-specific flood design parameters.

SEISMIC LOADS

Seismic design shall be in accordance with IBC and ASCE 7.

FOUNDATIONS

Deep foundations, such as auger-cast piles or driven precast piles, are considered likelyin order to support the superstructure. Pile design shall be in accordance with ACI 318 and ASCE 24.

Cast-in-place concrete pile caps shall be provided at each building column and load-bearing wall, varying in size and geometry based upon loading and pile-group configuration. The top of pile caps shall be below finished first floor elevation to allow for utilities and sloped floor to drains.

The D-BC shall be responsible for employing a registered professional engineer familiar with typical construction practices in the local areato prepare a geotechnical report for this project. The foundation design shall be based on the recommendations made in this report. Foundations from the existing structures to be demolished by the Governmentwill be left inplace. The D-BC shall take their locations into account when locating new foundations.

GARAGE LEVEL CONSTRUCTION

The first floor of the building is a parking level that shall be comprised of a slab-on-grade unless a structurally supported slab is warranted due to potential flooding effects of erosion and scour. Both options shall be evaluated and discussed with the Government and the geotechnical engineer prior to making a final decision. In either case, slope concrete to floor drains.

Concrete curbs shall be utilized around stairs and elevators to protect pedestrians from vehicles. Pre-cast concrete wheel stops or concrete curbs shall be provided at each parking space. Stairs and elevator shafts shall be protected from vehicles. Exposed concrete walls shall be smooth formed finish and painted.

SUPERSTRUCTURE

The superstructure (including the Community Level, typical residential floors, and roof) shall be structural steel or concrete construction. While framing is expected to be repetitive at the typical residential floors, the community level framing may require more complex framing arrangements such as transfer girders and additional load-bearing walls and columns to transfer loads from the towers downward. These types of details are particularly important because Progressive Collapse provisions are in effect.

Unbonded post-tensioned concrete is not permitted on this project because Progressive Collapse design is required as indicated below.

EXTERIOR WALLS

Exterior walls as required per code to withstand hurricane and seismic forces.

SPECIAL CONSTRUCTION REQUIREMENTS

Progressive Collapse Design is mandatory for all GSA structures and shall be in accordance with current GSA standards. In some cases, the GSA guidelines allow “exemptions” from progressive collapse. However, exemption is unlikely to occur for this project because the perimeter frame is not likely to be designed for a high seismic design category. Given that the structure is less than 10-stories, linear procedures should be utilized for the analysis unless significant irregularities are encountered that require non-linear analyses.

The GSA Progressive Collapse procedure is based on instantaneous loss of various columns or load-bearing walls at the ground level. Losses may occur along perimeter edges, at corners, and at interior locations one at a time but not simultaneously at multiple locations. Three-dimensional computer programs are used to model various scenarios to preclude global collapse of the structure due to localized damage of a single column or wall. The design/analysis approachmay result in larger (i.e. wider, deeper, thicker)beams, girders, columns, and wallsthat are more heavily reinforced than in normal structures. This may also result in an increased building height and more robust foundations.

STRUCTURAL OBSERVATIONS

Additional structural observations are required for this project due to the high wind speed (IBC 1709.3). The D-BC will employ a registered design professional licensed in the State of Mississippito perform structural observations for general conformance to the approved construction documents at significant construction stages and at completion of the structural system.

BUILDING DEMOLITION

Given that the new facility could be constructed within the existing building footprint, it is the D-BC’s responsibility to coordinate their design with any existing foundations, abandoned utilities, or other potential hazards that could affect construction of the new foundation system, and remove or relocate such items as necessary.

General Services AdministrationC - 1Public Buildings Service

Southeast Sunbelt RegionChapter 7Real Estate Design and Construction

UNCLASSIFIED