Design of Residential Buildings in (High- Wind) Coastal Areas

2012

Instructor: Jeffrey Havelin, PE

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12-1COASTAL CONSTRUCTION MANUAL

CHAPTER 12DESIGNING THE BUILDING

12.1 The Design Process The design process begins with the loads that were determined from the formulas developed and discussed in Chapter 11. These loads then must be applied to the building; forces and stresses will be determined from these loads, and resistance to the forces and stresses in the form of connectors and materials will be selected. Figure 12-1 illustrates the general design process.

Each step of this process is covered as a separate section of this chapter. The many variations of designs, the location of buildings in different hazard areas, the varieties of building shapes, and other building parameters are discussed where appropriate in each of the design steps. A building located in either a V zone or a coastal A zone that is subject primarily to flood and wind hazards is used throughout this chapter as a demonstration of how to design a building in a coastal flood hazard area.

Determine loads; use codes, standards, experience, judgment; state givens and assumptions.

Determine forces at connections and stresses on components; apply through vertical and horizontal load paths.

Specify connectors or connection methods to satisfy load conditions; specify materials that meet stress levels.

Note design assumptions on drawings; specify design details on drawings.

Apply loads to building starting at the top; assume a building type, frame, and materials;

assume a design approach (ASD, strength).

Designing the Building

Figure 12-1 Coastal construction design process.

NOTE Designers should consider the consequences of damage to, or the failure of, critical design components.

12-2 FEDERAL EMERGENCY MANAGEMENT AGENCY

CHAPTER 12 DESIGNING THE BUILDING

The design process involves the following:

• determining design loads

• determining the building’s foundation, structural frame, and envelope

• determining the connections between individual elements

• determining the elevation, placement, and support for utilities

• selecting the appropriate materials

The entire design process is based on the fundamental premise that anticipated service and natural hazard loads can and must be transferred through the building in a continuous path to the supporting soils. ANY weakness in that continuous path is a potential point of failure of the building, and any failure creates the possibility for large property losses and the potential for loss of life.

This manual does not cover all of the almost endless number of combinations of loads, materials, building shapes and functions, hazard zones, and elevations. The designer will find that engineering judgment will need to be applied to a range of problems during the design of a coastal residential building. Therefore, it is the intent of this manual to provide sufficient background and examples so that a designer can effectively design a residential building for construction in a coastal hazard area.

In this manual, the recommended design method is Allowable Stress Design (ASD), so there are factors of safety (FS) built into the development of the material stresses and the forces at the connections. This design method has been chosen for this manual because ASD continues to be the predominant design method in light-frame, residential, wood construction. Most suppliers of wood framing hardware and connectors provide load limits for their products with factors of safety built into the limits. Load and Resistance Factor Design (LRFD) guidance is available for wood if the designer prefers this ultimate strength or limit state design method.

12.2 Step 1 – Determining Loads The types of loads that most commonly act on one- to three-story residential buildings during severe natural hazard events are as follows:

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