Hsx Story Height Below Level X

Masonry cantilever shear wall structuresc a hsx is the story height below level x. b There shall be no drift limit for single-story structures with interior walls, partitions, ceilings, and exterior wall systems that have been designed to accommodate the story drifts. The structure separation requirement of Section 9.5.2.8 is not waived. c Structures in which the basic structural system consists of masonry shear walls designed as vertical elements cantilevered from their base of foundation...

Floor Vibrations 861 General Discussion

Building floors are subjected to a variety of vibrational loads that come from building occupancy. Although almost all loads except dead loads are nonstatic, internal sources of vibration that might be a cause of concern in an office or a residential building are the oscillating machinery, passage of vehicles, and various types of impact loads such as those caused by dancing, athletic activities, and even pedestrian traffic. The trend in the design of floor framing systems of high rises is for...

Info

Encased composite column design shear strength parameters. Elastic properties of composite elements can be transformed into equivalent properties of steel for stiffness analyses using standard procedures. As with steel or concrete frames, it may be more accurate to include a finite rigid joint size in the frame model, particularly when the composite columns are quite large. The design of composite ordinary moment-resisting frames is not significantly different from the procedures...

Example Projects

Buildings with Composite Steel Pipe Columns Examples of buildings with large-diameter composite columns are shown in Figs. 5.15, 5.16 and 5.17. The 44-story Pacific First Center has eight 7.5-ft (2.3-m)-diameter pipe columns in the core and several 2.5-ft (0.76-m)-diameter columns at the perimeter, each filled with 19-ksi (131-Mpa) concrete. The second example is a 62-story tower with 9-ft (2.7-m)-diameter pipe columns tied together with 10-story-high X-braces. The third is a 58-story...

Deformation Compatibility

The 1994 Northridge earthquake taught a number of lessons in seismic design, one of which is the importance of satisfying the so-called deformation compatibility requirement. This requirement, extensively revised in 1997 UBC after observations from the Northridge earthequake, strives to achieve parity in seismic performance of framing elements and connections not required by design to be part of lateral-force-resisting systems, with those required by design. This is because we know now, from...

Seismic Rehabilitation of Existing Buildings

Seismic rehabilitation of a building entails costs as well as disruption of its usage. In fact, the effects of a rehabilitation program are similar to those of an earthquake because strengthening, in terms of cost and the need to vacate the structure while strengthening is underway, is analogous to building repair after an earthquake. The crucial difference is that strengthening occurs at a specified time and no deaths or injuries will occur during the process. In a seismic rehabilitation study...

Bucklingrestrained Braced Frame

Buckling-restrained brace frames (BRBFs) have a high degree of ductility (energy absorbing capability) and good lateral stiffness, and are relatively simple to repair after a major earthquake. Unbonded braced frames, which may be considered a special class of BRBFs, consist of a steel core installed within an outer shell with mortar infill between the plate and the shell. An unbonding agent is applied to the core plate to prevent it from transmitting axial load to the buckling-restraining...

Alternate Design Philosophy

Although earthquake performance objectives are implicit in building codes, significant questions linger. Is the philosophy of inferring the behavior adequate to define the expected earthquake performance Can the performance be actually delivered Should the earthquake response objectives be explicitly stated in building codes Is it feasible to make an existing nonductile building conform to current detailing and ductility provisions If not, what level of upgrade will provide for minimum life...

Chapter Summary

Since earthquakes can occur almost anywhere, some measure of earthquake resistance in the form of reserve ductility and redundancy should be built into the design of all structures to prevent catastrophic failures. The magnitude of inertial forces induced by earthquakes depends on the building mass, ground acceleration, and the dynamic response of the structure. The shape and proportion of a building have a major effect on the distribution of earthquake forces as they work their way through the...

Seismic Design

Structural design of buildings for seismic loading is primarily concerned with structural safety during major earthquakes, but serviceability and the potential for economic loss are also of concern. Seismic loading requires an understanding of the structural behavior under large inelastic, cyclic deformations. Behavior under this loading is fundamentally different from wind or gravity loading, requiring much more detailed analysis, and application of a number of stringent detailing requirements...

Composite Buildings

It is worth noting, for the sake of humility, that the basic ideas of composite behavior were conceived and attempts at composite construction made long before anyone reading this work was born. In the United States, composite construction first appeared in 1894. In that year, Joseph Milan, an engineer from Vienna, built a composite bridge in Rock Rapids, IA, using steel I-beams bent into an arch shape, and then encasing concrete around them he claimed that steel and concrete acted together. So...

Building Deformations

The basic design procedure for new structures consists of the selection of lateral forces appropriate for design purposes, and then providing a complete, appropriately detailed, lateral-force-resisting system to carry these forces from the mass levels to the foundations. Although deformations are checked, experience has shown that new structures with modern materials and ductile detailing can sustain large deformations while experiencing limited damage. Older structures, however, do not have...

Trussed Tube

A trussed tube system improves on the efficiency of the framed tube by increasing its potential for use in taller buildings and allowing greater spacing between the columns. This is achieved by adding diagonal bracing at the faces of the tube to virtually eliminate the shear lag in both the flange and web frames. The framed tube, as discussed previously, even with its close spacing of columns is somewhat flexible because the high axial stresses in the columns parallel to the lateral loads...

Moment Frames

The Northridge earthquake demonstrated that the pre-1994 prescriptive connection shown in Fig. 3.3 was inadequate for anticipated seismic demands. Following that earthquake, a number of steel moment-frame buildings were found to have experienced brittle fractures of beam-to-column connections, shattering the belief that steel moment-frame buildings were essentially invulnerable to earthquake-induced structural damage. It was also thought that should such damage occur, it would be limited to...

Component Behavior

Nonstructural components can be classified as deformation-or acceleration-sensitive. If the performance of a component is controlled by the supporting structure's deformation, such as the interstory drift, it is deformation-sensitive. Curtain walls and piping systems running floor-to-floor are some examples of deformation-sensitive components. These components spanning from floor-to-floor are often rigidly connected to the structure. They are thus deformation-sensitive and are susceptible to...

Irregular Buildings

The seismic design of regular buildings is based on two concepts. First, the linearly varying lateral force distribution is a reasonable and conservative representation of the actual response distribution due to earthquake ground motions. Second, the cyclic inelastic deformation demands are reasonably uniform in all of the seismic force-resisting elements. However, when a structure has irregularities, these concepts may not be valid, requiring corrective factors and procedures to meet the...

Code Provisions For Seismic Upgrade

Most building codes deal primarily with the design of new buildings. For seismic upgrade, the primary use for these documents is determining existing building capacity. They do not, in general, provide guidance for evaluating and upgrading the seismic resistance of an existing building. Most codes allow existing buildings to use their current lateral-load-resisting systems if only trivial changes to the structure are proposed and the building's use remains unchanged. Codes require upgrading of...

ASCE 702 Detail Description of Seismic Provisions

Engineers who design and detail structures for many areas of the United States with low seismic risk have not had to deal with design and detailing requirements that apply to moderate and high seismic zones on the west coast. But that may change due to major revisions of seismic provisions published in ASCE 7-02. Traditionally, the magnitude of the seismic force and level of seismic detailing were strictly a function of structure location. With the latest seismic design provisions, these are...

Design and Detailing Requirements

The seismic design and detailing requirements are cascading meaning that requirements pertaining to a lower category also apply to a higher category. Therefore, SDC A requirements also apply to SDC B, SDC B to SDC C, and so on. 2.4.5.1. Seismic Design Category A (ASCE 7-02 Sect. 9.5.2.6.1) Design and detailing of structures with a complete and identifiable load path for seismic forces is mandatory. Other requirements are 1. Tie smaller portions of structure to the main structure using a design...

Seismic Design Highlights ASCE 702 IBC03 NFPA 5000

ASCE 7-02 utilizes spectral response seismic design maps to quantify seismic hazards on the basis of the contours. These maps were prepared by the U.S. Geological Survey (USGS), along with a companion CD-ROM. This CD-ROM provides mapped spectral values for a specific site based on the site's longitude, latitude, and site soil classification. Examples are shown in Figs. 2.43 and 2.44. Longitude and latitude for a given address can be found at Web sites such as www.Oeocode.com. Use of the CD-ROM...

Characteristics Of Wind

The flow of wind is complex because many flow situations arise from the interaction of wind with structures. However, in wind engineering, simplifications are made to arrive at design wind loads by distinguishing the following characteristics Variation of wind velocity with height. Vortex shedding phenomenon. Dynamic nature of wind-structure interaction. 1.3.1. Variation of Wind Velocity with Height The viscosity of air reduces its velocity adjacent to the earth's surface to almost zero, as...

Kr

0.85 x 0.0024 x 98.5 x 394 x 1.3 x 1302 3.814 x 0.363 1.384 ft sec2 1.384 x 31.11 milli-g 43 milli-g This is the maximum along-wind acceleration (1.49) This is more than twice the threshold value of 20 milli-g. Therefore, it is important to verify the results by conducting wind tunnel tests. If the test results confirm the likelihood of the building experiencing high accelerations, adding dampers to the building to reduce building oscillations is an option. This is discussed in Chapter 8....

Dynamic Analysis Theory

A good portion of the loads that occur in buildings can be considered static, requiring static analysis only. Although almost all loads except dead loads are transient, meaning that they change with time, it is customary to treat them as static. For example, lateral loads imposed by transient wind pulses are usually treated as static loads and even in earthquake design, one of the acceptable methods of design, particularly for buildings with regular configuration, is to use an equivalent static...

Aeroelastic Study

Aeroelastic model study attempts to take the guesswork out of the gust factor computation by measuring directly the magnitude of dynamic loads. These are measured using a variety of models ranging from very simple rigid models mounted on flexible supports to models exhibiting the multimode vibration characteristics of tall buildings. The more common types of models used in aeroelastic studies can be broadly classified into two categories 1) stick models and 2) multi degree-of-freedom models. In...

Composite Gravity Systems

Gravity systems in composite construction can be broadly classified into composite floor systems and composite columns. Composite floor systems can consist of simply supported prismatic or haunched structural steel beams, trusses, or stub girders linked via shear connectors to a concrete floor slab to form an effective T-beam flexural member. Formed metal deck supporting a concrete topping slab is an integral component in these floor systems used nearly exclusively in steel framed buildings in...

Rigid Frames Moment Frames

Seismic Design Criterion

A frame is considered rigid when its beam-to-column connections have sufficient rigidity to hold virtually unchanged the original angles between intersecting members. In this system, shown in Fig 3.2, lateral loads are resisted primarily by the rigid frame action that is, by the development of shear forces and bending moments in the frame members and joints. The continuity at both ends of beams also assists in resisting gravity loads more efficiently by reducing positive moments in beam spans....

Differential Shortening Of Columns

Columns in tall buildings experience large axial displacements because they are relatively long and accumulate gravity loads from a large number of floors. A 60-story interior column of a steel building, for example, may shorten as much as 2 to 3 in. (50 to 76 mm) at the top, while a concrete column of similar height may experience an additional 2 to 3 in. (50 to 76 mm) of shortening due to creep and shrinkage of concrete. If such shortening is not given due consideration, problems may develop...

Pedestrian Wind Studies

A sheet of air moving over the earth's surface is reluctant to rise when it meets an obstacle such as a tall building. If the topography is suitable, it prefers to flow around the building rather than over it. Some examples are shown in Fig.1.30. There are good physical reasons for this tendency, the predominant one being that wind, if it has to pass an obstacle, will find the path of least resistance, i.e., a path that requires minimum expenditure of energy. As a rule, it requires less energy...

Composite Elements

The primary structural components used in composite building construction consist of the following horizontal and vertical elements In steel buildings, the use of high-strength, light-gauge (16- to 20-gauge) metal deck with concrete topping has become the standard floor-framing method. The metal deck has embossments pressed into the sheet metal to achieve composite action with the concrete topping. Once the concrete hardens, the metal deck acts as the bottom tension reinforcement while the...

Six Component Of Wind

Strouhal Number Vortex Shedding

A wind velocity having a specific mean recurrence interval. Mean recurrence intervals of 20 and 50 years are generally used in building design, the former interval for determining the comfort of occupants in tall buildings subject to wind storms, and the latter for designing lateral resisting elements. In general, wind buffeting against a bluff body gets diverted in three mutually perpendicular directions, giving rise to forces and moments about the three directions. Although all six...

Concrete Shear Walls

Shear Key Dimensions

The problems that are most difficult to fix are those caused by the irregular configuration of a building (e.g., abrupt changes in stiffness, soft stories, large floor openings, and reentrant floor corners). These cases may require the addition of vertical or horizontal rigid structural elements, as well as strengthening of existing foundations or addition of new ones. There are several approaches to the reinforcement of existing concrete shear walls, discussed in the following sections. Wall...

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...

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

Outrigger Belt Truss

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

Moment Resisting Frame System

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

Lateral Elevation Building

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

Cable Bracing System

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

Tuned Liquid Column Damper Tlcd

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...

Asce 702 Ibc 2003 And Nfpa 5000 Seismic Provisions

Before discussing the seismic provisions of the above referenced standards, it is instructive to briefly dwell on their evolution, particularly in the United States. The code development process for seismic provisions is less than 80 years old. In 1926, the Pacific Coast Building Officials published the first edition of the Uniform Building Code UBC with nonman-datory seismic provisions that appeared only in an appendix. They included only a few technical requirements consisting of design for a...

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

Asce Basic Wind Speeds Maps

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

Typical Bending Moment Diagrams

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...