1. Seismic Use Group According to the nature of Building Occupancy, each structure is assigned a Seismic Use Group (I, II, or III) and a corresponding Occupancy Importance (I) factor (I  1.0, 1.25, or 1.5). Seismic Use Group I structures are those not assigned to either Seismic Use Group II or III. Seismic Use Group II are structures whose failure would result in a substantial public hazard due to occupancy or use. Seismic Use Group III is assigned to structures for which failure would result in loss of essential facilities required for post-earthquake recovery and those containing substantial quantities of hazardous substances. 2. Site Class Based on the soil properties, the site of building is classified as A, B, C, D, E, or F to reflect the soil-structure interaction. Refer to IBC 2000 for Site Class definition. 3. Spectral Response Accelerations SS and S1 The spectral response seismic design maps reflect seismic hazards on the basis of contours. They provide the maximum considered earthquake spectral response acceleration at short period SS and at 1-second period S1. They are for Site Class B, with 5% of critical damping. Refer to the maps in IBC 2000. 4. Basic Seismic-Force-Resisting System Different types of structural system have different energy-absorbing characteristics. The response modification coefficient R in Table 5.9 is used to account for these characteristics. Systems with higher ductility have higher R values. With the above basic parameters available, the following design and analysis criteria

At least two No. 5 bars should be placed around all window and door openings. The bars should extend at least 24 in beyond the corners of openings. Design for Eccentric Loads. Bearing walls with bending moments sufficient to cause tensile stress must be designed as columns for combined flexure and axial load, including slenderness effects if applicable. Minimum reinforcement areas and maximum bar spacings are the same as for walls designed by the empirical method. Lateral ties, as for columns, are required for compression reinforcement and where the vertical bar area exceeds 0.01 times the gross horizontal concrete area of the wall. (For column capacity, see Art. 9.82.) Under the preceding provisions, a thin, wall-like (rectangular) column with a steel ratio less than 0.01 will have a greater carrying capacity if the bars are detailed as for walls. The reasons for this are: The effective depth is increased by omission of ties outside the vertical bars and by the smaller cover (as small as 3/4 in) permitted for vertical bars in walls. Furthermore, if the moment is low (eccentricity less than one-sixth the wall thickness), so that the wall capacity is determined by Eq. (9.82), the capacity will be larger than that computed for a column, except where the column is part of a frame braced against sidesway. If slenderness effects need to be considered, slender walls must comply with the slenderness requirements for columns (Art. 9.86). For slender precast concrete wall panels, where the panels are restrained at the top, an alternative design procedure can be used. The alternative approach was introduced into Chapter 14 of the ACI 318-99 Building Code. Complying with the provisions in the alternative procedure is deemed to satisfy the Codes slenderness requirements for columns. Nonbearing reinforced-concrete walls, frequently classified as panels, partitions, or cross walls, may be precast or cast in place. Panels serving merely as exterior cladding, when precast, are usually attached to the columns or floors of a frame, supported on grade beams, or supported by and spanning between footings, serving as both grade beams and walls. Cast-in-place cross walls are most common in substructures. Less often, cast-in-place panels may be supported on grade beams and attached to the frame. In most of these applications for nonbearing walls, stresses are low and alternative materials, such as unreinforced masonry, when supported by beams above grade, or panels of other materials, can be used. Consequently, unless esthetic requirements dictate reinforced concrete, low-stressed panels of reinforced concrete must be designed for maximum economy. Minimum thickness, minimum reinforcement, full benefits of standardization for mass-production techniques, and design for double function as both wall and deep beam must be achieved. Thickness of nonbearing walls of reinforced concrete should be at least onethirtieth the distance between supports, but not less than 4 in. The ACI 318 Building Code, however, permits waiving all minimum arbitrary requirements for thickness and reinforcement where structural analysis indicates adequate strength and stability. Where support is provided, as for a panel above grade on a grade beam, connections to columns may be detailed to permit shrinkage. Friction between base of panel and the beam can be reduced by an asphalt coating and omission of dowels. These provisions will permit elimination or reduction of horizontal shrinkage reinforcement. Vertical reinforcement is seldom required, except as needed for spacing the horizontal bars. If a nonbearing wall is cast in place, reinforcement can be nearly eliminated except at edges. If the wall is precast, handling stresses will often control. Multiple pickup points with rigid-beam pickups will reduce such stresses. Vacuum pad pickups can eliminate nearly all lifting stresses. Where deep-beam behavior or wind loads cause stresses exceeding those permitted on plain concrete, the ACI 318 Building Code permits reduction of minimum tension-reinforcement [As
200bd/y (Art. 9.46)] if reinforcement furnished is onethird greater than that required by analysis. (For deep-beam design, see Art. 9.88.) Under the ACI 318 Building Code, cantilever retaining walls are designed as slabs. Specific Code requirements are not given for cantilever walls, but when axial load becomes near zero, the Code requirements for flexure apply. FIGURE 9.38 Factored loads and critical sections for design of cantilever retaining

A building is an assemblage that is firmly attached to the ground and that provides total or nearly total shelter for machines, processing equipment, performance of human activities, storage of human possessions, or any combination of these. *Revised and updated from the previous edition by the late Frederick S. Merritt. Building design is the process of providing all information necessary for construction of a building that will meet its owners requirements and also satisfy public health, welfare, and safety requirements. Architecture is the art and science of building design. Building construction is the process of assembling materials to form a building. Building design may be legally executed only by persons deemed competent to do so by the state in which the building is to be constructed. Competency is determined on the basis of education, experience, and ability to pass a written test of design skills. Architects are persons legally permitted to practice architecture. Engineers are experts in specific scientific disciplines and are legally permitted to design parts of buildings; in some cases, complete buildings. In some states, persons licensed as building designers are permitted to design certain types of buildings. Building construction is generally performed by laborers and craftspeople engaged for the purpose by an individual or organization, called a contractor. The contractor signs an agreement, or contract, with the building owner under which the contractor agrees to construct a specific building on a specified site and the owner agrees to pay for the materials and services provided. In the design of a building, architects should be guided by the following principles: 1. The building should be constructed to serve purposes specified by the client. 2. The design should be constructable by known techniques and with available labor and equipment, within an acceptable time. 3. The building should be capable of withstanding the elements and normal usage for a period of time specified by the client. 4. Both inside and outside, the building should be visually pleasing. 5. No part of the building should pose a hazard to the safety or health of its occupants under normal usage, and the building should provide for safe evacuation or refuge in emergencies. 6. The building should provide the degree of shelter from the elements and of control of the interior environmentair, temperature, humidity, light, and acoustics specified by the client and not less than the minimums required for safety and health of the occupants. 7. The building should be constructed to minimize adverse impact on the environment. 8. Operation of the building should consume a minimum of energy while permitting the structure to serve its purposes. 9. The sum of costs of construction, operation, maintenance, repair, and anticipated future alterations should be kept within the limit specified by the client. The ultimate objective of design is to provide all the information necessary for the construction of a building. This objective is achieved by the production of drawings, or plans, showing what is to be constructed, specifications stating what materials and equipment are to be incorporated in the building, and a construction contract between the client and a contractor. Designers also should observe construction of the building while it is in process. This should be done not only to assist the client in ensuring that the building is being constructed in accordance with plans and specifications but also to obtain information that will be useful in design of future buildings. Systems design comprises a logical series of steps that leads to the best decision for a given set of conditions. The procedure requires: Analysis of a building as a system. Synthesis, or selection of components, to form a system that meets specific objectives while subject to constraints, or variables controllable by designers. Appraisal of system performance, including comparisons with alternative systems. Feedback to analysis and synthesis of information obtained in system evaluation, to improve the design. The prime advantage of the procedure is that, through comparisons of alternatives and data feedback to the design process, systems design converges on an optimum, or best, system for the given conditions. Another advantage is that the procedure enables designers to clarify the requirements for the building being designed. Still another advantage is that the procedure provides a common basis of understanding and promotes cooperation between the specialists in various aspects of building design. For a building to be treated as a system, as required in systems design, it is necessary to know what a system is and what its basic characteristic are. A system is an assemblage formed to satisfy specific objectives and subject to constraints and restrictions and consisting of two or more components that are interrelated and compatible, each component being essential to the required performance