Windtunnel Engineering

Wind-tunnel testing of buildings has been an offshoot of aeronautical engineering, in which the flow of wind is duplicated at high altitudes. The tunnels for testing airplanes are designed to minimize the effects of turbulence, and as such, they do not duplicate atmospheric boundary layer or wind turbulence. This is because majority of airplane flights, except for brief periods of landing and takeoff, occur at a height well above the boundary layer. Building activity, on the other hand, occurs...

Simple Pendulum Damper

The principle feature of the system shown in Fig. 8.30h is a mass block slung from cables with adjustable lengths. The mass typically represents approximately 1.5 to 2 of the building's generalized mass in the first mode of vibration. The mass is connected to hydraulic dampers that dissipate energy while reducing the swinging motions of the pendulum. The adjustable frame is used as a tuning device to tailor the natural period of vibration of the pendulum. The frame can be moved up and down and...

Info

Structural systems for concrete buildings. Figure 4.1. Structural systems for concrete buildings. rows of joists commonly formed by using square domes. The domes are omitted around the columns to increase the moment and shear capacity of the slab. Any of the three systems may be used as an integral part of a lateral resisting system and all are popular for apartments and hotels in areas of low seismicity. The slab system shown in Fig. 4.2 has two distinct actions in resisting...

Mechanical Properties of Seismic Isolation Systems

A seismic isolation system is the collection of all individual seismic isolators and may be composed entirely of one type of seismic isolator, a combination of different types of seismic isolators, or a combination of seismic isolators acting in parallel with energy dissipation devices (i.e., a hybrid system). The most popular devices for seismic isolation in the United States may be classified as either elastomeric or sliding. Examples of elastomeric isolators include high-damping rubber...

Steel Beam And Steel Column Without Concrete Encasement

Composite Construction Column Junction

Steel zipper column resists unbalanced post-buckling forces in the braces. Figure 5.33. Composite concentrically braced frames (a) V-bracing (b) inverted V-bracing (c) X-bracing (d) diagonal bracing (e) two-story X-bracing (f) zipper column with inverted V-bracing. Composite braces of either concrete-filled steel tubes or concrete-encased steel braces may be combined with steel frame elements. Composite columns may also be used in conjunction with composite floors and steel bracing members, as...

Interacting System Of Braced And Rigid Frames

Suspension Structure Building

Even for buildings in the of 10- to 15-story range, unreasonably heavy columns may result if the lateral bracing is confined to the building's service core because the depth available for bracing is usually limited. Additionally, high uplift forces may occur at the bottom of core columns, presenting foundation problems. For such buildings, an economical structural system can be devised, using a combination of rigid frames with a core bracing system. Although relatively deep girders are required...

Ei

Vierendeel Truss Detail Section

Camber beam for 75 of calculated unshored condition. Therefore camber specified 1.78 x 0.75 1.34, say, 1.25 in. Deflection under superimposed dead and live loads for Figure 7.58. Schematic floor plan showing haunch girders. Figure 7.58. Schematic floor plan showing haunch girders. Compared to L 360 40 x 12 360 1.33 in., the calculated deflection of 0.84 in. is small. Therefore the design is OK. It should be noted that the lowest percentage of partial composite allowed by the AISC specifications...

First Interstate World Building Los Angeles Floor Plan

Concentric Braces Passing Steel Decks

Nations Bank Plaza, Atlanta, GA (a) building elevation (b) typical framing plan (c) section. The core columns are braced on all four sides with diagonal bracing as shown schematically in Fig. 8.15c. Since the braces are arranged to clear door openings in the core, their configuration is different on all four sides. Steel girders 36 in. (0.91 m) deep are moment-connected between the composite columns to transfer part of the overturning moment to the exterior columns. Because the...

Lateral ForceResisting Systems

Load Path Lateral

There are several systems that can be used effectively for providing resistance to seismic lateral forces. Some of the more common systems are shown in Fig. 2.6. All of the systems rely on a complete, three-dimensional space frame a coordinated system of moment frames, shear walls, or braced frames with horizontal diaphragms or a combination of the systems. 1. In buildings where a space frame resists the earthquake forces, the columns and beams act in bending. During a large earthquake,...

Case Studies

Petronas Towers Plan

Having noted that a building must have a system to resist both lateral bending and shear in addition to the ever-present gravity loads, let us take a trip around the world to explore how prominent engineers have exploited this concept. Although some of the case studies include run-of-the-mill designs that a large number of engineers solve on a day-to-day basis, others are once-in-a-lifetime high-profile projects, even daring in their engineering solutions. Many are examples of buildings...

Seismic Importance Factor IE

In seismic design, the importance factor I is used to increase the margin of safety against collapse. For example, I 1.50 for essential facilities, I 1.25 for hazardous facilities, and I 1.15 for special occupancy structures. Essential structures are those that must remain operative immediately following an earthquake such as emergency treatment areas and fire stations. Hazardous facilities include those housing toxic or explosive substances. Examples of special occupancy structures are those...

Seismic Strengthening Details

Concrete Frame Building Section

A thorough understanding of existing construction and seismic retrofit objectives acceptable to owners and to the building official is an important consideration before a seismic retrofit is undertaken. The importance of considering global and elemental deformations at expected levels of seismic forces, not at code or design levels, cannot be overstressed. This is because even with the use of amplification factors, the deformations are at best an approximation, particularly when applied to...

Composite Building Systems

Shear Wall Intersections

Composite building systems may be classified into the following categories 1. Composite shear wall system. 2. Composite shear wall-frame interacting system. 4. Composite vertically mixed system. 5. Composite mega frames with super columns. Figure 5.7. Moment transfer between steel beam and concrete wall. Figure 5.7. Moment transfer between steel beam and concrete wall. Figure 5.8. Composite shear walls with steel plates (a) plan (b) section. Figure 5.8. Composite shear walls with steel plates...

Tuned Liquid Column Damper

A tuned liquid column damper (TLCD) is in many ways similar to a TMD that uses a heavy concrete block or steel as the tuned mass. The difference is that the mass is now water or some other liquid. The damper is essentially a tank in the shape of a U. It has two vertical columns connected by a horizontal passage and filled up to a certain level with water or other liquid. Within the horizontal passage, screens or a partially closed sluice gate are installed to obstruct flow of water, thus...

Selected References

Farzad Naeim, ed., The Seismic Design Handbook. New York Van Nostrand Reinhold, 1989. 2. Uniform Building Code, International Code Council, 1991, 1994, and 1997. 3. American National Standards Institute (ANSI) A58.1, Washington, DC, 1982. 4. Structuring Tall Buildings, Progressive Architecture, vol. 61 no. 12, December 1980. 5. J. E. Cermak, Applications of Fluid Mechanics to Wind Engineering, Journal of Fluids Engineering, vol. 97, p. 9, March 1975. 6. Wind Effects on High Rise Buildings,...

Seismic Design Example Static Procedure IBC 2003 ASCE 702 NFPA 5000

A 12-story building located in downtown, Los Angeles, California. The building properties summarized in Fig. 2.46 are the same as those used in the 1997 UBC example, Section 2.13.19.1. Occupancy group II (Table 2.13 ASCE Table 1.1) SUG 1 (Tble 2.12 ASCE Table9.1.3) SDC D (Tables 2.17 and 2.18 ASCE Tables 9.4.2.1a and b) Site class as determined by project geotechnical engineer D Figure 2.46. Design example ASCE 7-02 (IBC-03), static force procedure. Figure 2.46. Design example ASCE 7-02...

Seismic Isolation

Seismic Isolation Base Cabinets

Seismic isolation is a viable design strategy that has been used for seismic rehabilitation of existing buildings and in the design of a number of new buildings. In general, this system will be applicable to the rehabilitation and design of buildings whose owners desire superior earthquake performance and can afford the special costs associated with the design, fabrication, and installation of seismic isolators. The concepts are relatively new and sophisticated, and require more extensive...

Tall Buildings

Tall buildings have fascinated humans from the beginning of civilization as evidenced by the pyramids of Giza, Egypt Mayan temples of Tikal, Guatemala and Kutub Minar of Delhi, India. The motivation behind their construction was primarily for creating monumental rather than human habitats. By contrast, contemporary tall buildings are primarily a response to the demand by commercial activities, often developed for corporate organizations as prestige symbols in city centers. The feasibility of...

Code Provisions For Wind Loads

In recent years, wind loads specified in codes and standards have been refined significantly. This is because our knowledge of how wind affects buildings and structures has expanded due to new technology and advanced research that have ensued in greater accuracy in predicting wind loads. We now have an opportunity to design buildings that will satisfy anticipated loads without excessive conservatism. The resulting complexity in the determination of wind loads may be appreciated by comparing the...

Panel Zone Effects

Shear Deformation

Structural engineers involved in the design of high-rise structures are confronted with many uncertainties when calculating lateral drifts. For example, they must decide the magnitude of appropriate wind loads and the limit of allowable lateral deflections and accelerations. Even assuming that these are well defined, another question that often comes up in modeling of building frames is whether or not one should consider the panel zones at the beam-column intersections as rigid. The panel zone...

National Building Code of Canada NBCC 1995 Wind Load Provisions

Pressure Coefficient Wind Buildings

The reader may be wondering why, after an arguably extensive coverage of the ASCE 7-02 wind load provisions, the author would burden the text with yet another building code provision. The reason is simple Although extensive in its treatment of wind, the ASCE 7-02 does not provide an analytical procedure for estimating across-wind response of tall, flexible buildings. To the best of the author's knowledge, NBCC is the only code in North America that presents an analytical method for computing...