Showing papers on "Shear wall published in 1995"

A noninvasive method to estimate wall shear rate using ultrasound.

Abstract: Wall shear stress (blood viscosity x wall shear rate), imposed by the flowing blood, and blood pressure are the main mechanical forces acting on a blood vessel wall. Accurate measurement of wall shear stress is important when investigating the development of vascular disease, since both high and low wall shear stresses have been cited as factors leading to vessel wall anomalies. Furthermore, in vitro studies have shown that endothelial cells, which play a key role in the function of the underlying arterial wall, undergo a variety of structural and functional changes in response to imposed shear stress. However, there is practically no knowledge about the influence of wall shear stress on the arterial wall in vivo because of the difficulty in measuring this stress in terms of magnitude and time variation. The method presented in this article to measure the time-dependent wall shear rate in the main arteries is based on the evaluation of velocity profiles determined by means of ultrasound, using off-line signal processing. Pulsed ultrasound is well suited for this application since it is noninvasive. The processing performed in the radio-frequency (RF) domain consists of a mean frequency estimator preceded by an adaptive vessel wall filter. In a pilot study (30 measurements in the carotid artery of five healthy volunteers) we investigated the reproducibility of our method to estimate wall shear rate as compared with the reproducibility of the measurement of blood flow velocity in the middle of the vessel. The coefficient of variation was on the order of 9% for blood flow velocity estimation, and for wall shear rate estimation on the order of 5%.

Performance of Buildings With Shear Walls in Earthquakes of the Last Thirty Years

Abstract: The author describes observations of shear wall performance in severe earthquakes in which modern reinforced concrete buildings stood the test of violent shaking, starting with the Chilean earthquake of May 1960 through most of the subsequent strong earthquakes, up until the Armenian earthquake of December 1988. Despile the excellent behavior of shear wall-type concrete structures as compared to concrete frame-type structures, building codes continued, up until the last decade, to give preference to concrete ductile frame structures (which are subject to higher distortions) while placing a substantial penally on the use of shear walls. This code approach was due to the lack of experimental and analytical background information on shear wall behavior. While a large body of information on shear walls accumulated during the 1980s, still more experimental and analytical studies are needed to create a solid basis for a rational seismic design approach. The availability of such information should encourage a wider use of shear walls for earthquake resistance

Horizontal Connections for Precast Concrete Shear Walls Subjected to Cyclic Deformations Part 1: Mild Steel Connections

Abstract: This paper represents the second part of a multiphase experimental program undertaken at the University of Manitoba to study the cyclic behavior of prestressed connections for precast concrete shear walls. The first part of the study dealt with the behavior of mild steel connections. In this paper, the results of testing five full-scale prestressed connections subjected to reversed cyclic combined flexure and shear loads are presented. The connections were also subjected to axial stresses normal to the connection to simulate gravity loads. The paper discusses the influence of cyclic vs. monotonic loading, use of prestressed strands vs. prestressed bars and the effect of fully unbonded prestressed bars on the behavior of the connections. Based on the test results, design recommendations for the prestressed connection in seismic zones are presented. A simple analytical procedure is developed to predict the envelope of cyclic response and a numerical design example is included to illustrate the design procedure.

Nonlinear Shear-Wall Analysis

Abstract: A finite-element program, WALSEIZ, capable of performing nonlinear analysis of a timber shear wall subjected to monotonic or dynamic loads is presented. Each wall is composed of four elements: a beam element to model the framing, a plate element to model the sheathing, nonlinear springs to model the sheathing-to-framing connectors (the load-displacement properties of which vary depending on whether monotonic or cyclic loads are applied), and a bilinear spring to model bearing between adjacent sheathing panels. The program can compute displacements at each of the nodes, forces, and stresses in each of the elements as a function of applied load for monotonic analysis and as a function of time for dynamic analysis. Results from the program are compared with experimental data to validate the program. The program is being used in investigations on the response of shear walls subjected to dynamic loads such as earthquakes and hurricanes.

Seismic Design of RC Structural Walls. Part I: New Code Format

Abstract: A displacement-based analytical procedure is used to develop a new code format for the seismic design of reinforced concrete shear walls. The procedure, which can be applied to walls of various cross-sectional shapes, uses a computed strain distribution to determine requirements for transverse reinforcement at wall boundaries for concrete confinement and to restrain buckling of reinforcement. Based on the computed strain distribution, both detailed and simplified approaches are presented to determine the amount and distribution of required transverse reinforcement. Simplified approaches are developed for symmetrically reinforced walls with axial load less than 0.10\iA\i\dw\if′\i\dc and for unsymmetrically reinforced walls with axial load less than 0.05\iA\i\dw\if′\i\dc. In addition, requirements for distribution of flexural strength over the height of the wall and limiting values for shear stress are also suggested. The proposed code format would increase design flexibility and could be incorporated into existing code formats.

State-of-the-Art Report on Seismic Performance of Unreinforced Masonry Buildings

Abstract: The author is commended for the summary of the progress in the reduction of earthquake hazard in unreinforced masonry buildings. However, the author repeats a common misunder­ standing of the Agbabian, Barnes, and Kariotis (ABK) methodology ("Methodology" 1984). The statement made in the ABK methodology is "over a realistic range of building and soil characteristics, the ground motion is transmitted through the end walls with little amplification." This statement is not equivalent to saying that these walls are infinitely rigid in plane. The ABK research studied the behavior of unreinforced masonry (URM) walls supported on flexible soils to support this assumption. The data obtained by the sensors placed in the Old Gilroy Fire Station ("Plots" 1990) support this assumption. The amplification of the ground displacements at the roof level was about 13 mm and 11 mm on a single pulse at the beginning of the record, and an average of 4 mm during the remaining period of ground shaking. This is a maximum amplification of the peak displace­ ment of 11 %. The amplification at the second-floor diaphragm was probably less than one-half of that at the roof as its height is 3.76 m above the base, and the height of the sensor at the roof above the base is 8.1 m. The studies by Tena-Colunga (1992) identified "that the dynamic response of the structure is controlled by the diaphragm action." And the diaphragm response is controlled by the input motion at its end. This is the key concept of the ABK methodology ("Methodology" 1984). The loading of the end shear wall results from its own mass and the diaphragm's dynamic response. There is no, and there need not be, assumption of rigid in-plane wall response. The inertial forces at any level in the end wall, applied to the end wall, are equal to the dynamic response forces of the diaphragm instead of to an arbitrarily assumed distribution of inertial forces. The discusser also disagrees with the assumption made by the author that the objective of the U.S. codes and standards used to reduce earthquake hazard is solely to mitigate the risk of life loss and injuries. The ABK methodology was not intended "solely to mitigate the risk of life loss or injuries." Mitigation of this risk is obtained by the reduction of property damage. The design-level ground motion used in the ABK research for the highest risk seismic zone had a spectral velocity of 0.76 mls ("Seismic" 1981). The design-level ground motion recommended in this highest-risk seismic zone by the Handbook for the Seismic Evaluation of Existing Buildings (FEMA 1992) is 0.61 mls for S2 type soils. The use of these codes and standards does meet historical pres­ ervation goals. It should be recognized that the predicted earthquake damage resulting from design-level earthquake has a small probability of occurrence. The discusser has seen many instances in which features of historic buildings were lost in an attempt to save them.

Seismic Design of RC Structural Walls. Part II: Applications

Abstract: Design calculations are presented for two shear-wall buildings using a new code format described in a companion paper. The lateral force resisting system for building 1 is comprised of two rectangular and two channel-shaped wall cross sections, and is typical of current U.S. practice of using relatively few walls for lateral load resistance. Based on the proposed code format, special transverse reinforcement is required at the boundaries of the rectangular wall; however, no special transverse reinforcement is required for the channel-shaped wall for loads parallel to the wall web. The lateral force resisting system for the second building is comprised of rectangular and T-shaped walls. Although no special transverse reinforcement is required for the rectangular walls, a moderate quantity of special transverse reinforcement is required for the web of the T-shaped wall. Wall design requirements for Building 1 are also compared with UBC 1991 design requirements. The design information presented for the two buildings reveals the flexibility and versatility of the proposed design format described in the companion paper, and indicates that the proposed design format will reduce construction materials and costs for most applications compared with current design requirements.

Shake-table tests of large-scale shear wall and infilled frame models.

Abstract: In order to evaluate and compare the seismic performance of different types of wall construction, three 1/3 scale four-storey models of structural walls were tested dynamically to ultimate failure by subjecting each of them to a sequence of simulated earthquakes of progressively increasing magnitude on a 5m x 5m shaking table. The three models tested are respectively : a reinforced concrete shear wall structure ; a masonry infilled reinforced-concrete frame structure ; and a concrete infilled frame structure.

Damping in low‐aspect‐ratio, reinforced concrete shear walls

Abstract: This report summarizes the information obtained from static and dynamic tests of scale-model Seismic Category 1 structures (exclusive of containment) on the damping of low-aspect-ratio, reinforced concrete shear walls. The report reviews experimental assessments of damping in low-aspect-ratio shear walls that have been reported in the literature and presents a summary of the types of structures and structural elements tested. It discusses the testing methods and the methods used to determine equivalent viscous damping ratios (both directly and indirectly), a numerical study that examines the accuracy of various methods for estimating damping from measured acceleration input and response data, and tabulates the damping results. The report concludes by graphically showing the changes in the damping of the shear walls as a function of the peak nominal base shear stress experienced by the structure during simulated seismic events. Also included are comparisons of the damping results obtained in this program with those obtained by other investigators.

Ductility of columns, wall, and beams -- how much is enough?

Abstract: Two hypothetical reinforced concrete buildings (one with special moment resisting frames and the other with structural walls) were designed. Using a time-history inelastic behavior approach, both buildings were analyzed. Drifts were determined for these structures when subjected to severe earthquakes similar to those expected in North America. In addition, drifts associated with an analysis based on ground motions measured for the 1985 Mexico City earthquake were also determined. Measured drifts from components detailed under 1990s North American code requirements are compared with calculated building drifts. These comparisons indicate that 1990s code requirements provide significantly more capacity than calculated to be needed for the structures and components considered. Finally, minimum drift requirements for components to be used in ductile frame buildings and in shear wall buildings are suggested.

Dynamic soil–structure interaction of coupled shear walls by boundary element method

Abstract: For a class of civil engineering structures, that can be accurately represented by ‘coupled shear walls’ (CSWs), a discrete model for the analysis of the dynamic interaction with the underlying soil is proposed. The CSWs, with one or more rows of openings, rest on a rigid foundation embedded in the elastic or viscoelastic half-space. A hierarchical finite element model based on an equivalent continuum approach is adopted for the structure. A frequency-domain boundary element method is used to represent the half-space. Finally, the set of equations governing the response of the coupled soil-structure system to harmonic lateral loads acting on the structure is also given. The frequency deviation effect with respect to the fixed-base structure and the effects of radiation and material damping in the soil are presented for different characteristics of the structure and different soil properties.

Efficient Modeling Scheme for Transient Analysis of Inelastic RC Structures

Abstract: Simple modeling schemes for efficient and reliable analysis of reinforced concrete structures in the inelastic range are presented. The objective of the modeling techniques is to represent overall behavior in terms of macromodels. A reinforced concrete structure is discretized into a series of macroelements: beam columns, shear walls, and general-purpose inelastic springs. Each element macro-model is developed from distributed flexibility concepts in which the effects of spread plasticity are implicitly included. Nonlinear material behavior is specified by means of hysteretic force-deformation models that incorporate stiffness degradation, strength deterioration, and pinching or bondslip effects. The models are incorporated into a microcomputer program that is capable of analyzing two-dimensional or entire three-dimensional wall-frame systems that can be discretized into a series of interconnected parallel frames. Solution modules for nonlinear static, monotonic, quasistatic cyclic, and transient seismic loads are developed. The efficiency and reliability of the modeling are demonstrated in terms of its effectiveness in reproducing experimentally observed behavior.

Compressive Strength Of Reinforced Masonry under Lateral Tension

Abstract: Shear walls are subjected to biaxial in-plane stresses when resisting seismic or wind loadings. Vertical tensile cracking reduces the compressive strength of walls in a direction normal to the tensile strain. This has been widely studied and accepted for reinforced concrete. However, for reinforced masonry there are no data available to predict the reduced compressive strength and behavior for walls with lateral tensile strains. To provide data for masonry, a biaxial test frame was constructed capable of loading masonry panels 80 cm (32 in.) high by 120 cm (48 in.) wide in combined compression and tension. Reinforced masonry panels subjected to various levels of lateral tensile strain were loaded to vertical compressive failure. Results from a test series of wall panels tested under various levels of lateral tension and vertical compression were used to establish a model to predict the reduction in compressive strength due to the lateral strain field.

Considérations sismiques des murs de refend ductiles avec ouvertures

Abstract: This paper describes the results of an analytical study of linear and nonlinear behaviour of ductile coupled shear walls with openings, under seismic loading. The walls in a typical building were studied and assumed to be ductile. They were designed, calculated, and detailed in compliance with the National Building Code of Canada 1990 (NBC) and the Canadian concrete code CAN3-A23.3-M84. The results of the elastic analysis show, as expected, that the concentrated force at the top specified by the NBC does not accurately simulate upper-mode effects, at least for this type of structure. A spectral analysis covering the five first modes, as described in the NBC, seems more suitable for coupled shear walls with openings with a period of more than 1.5 s approximately. The results of the nonlinear analysis show that application of the overstrength factor to the wall as recommended by CAN3-A23.3 greatly improves its behaviour and prevents tensile failure of the wall, although it does not always guarantee the desi...

Reduced rigidness structure of column base part and multistory shear wall subsidiary column base part

Abstract: PURPOSE:To improve the ductility of an outer peripheral column base part bearing high axial force on the first floor without injuring the degree of freedom of the design of floor planning, and to thereby also improve the ductility of the whole of a structural body CONSTITUTION:A column base reduced rigidness structure has such a formation as in a pure frame structure highrise building 1, a flat slab is used as an outer peripheral beam which joins to an outer peripheral corner column 2 and is on the first floor level and a beam which joins to an outer peripheral column from an inside column 6 except outer peripheral columns 5, 8 and is on the first floor level, or the beam is removed to reduce the rigidity on the first floor level of the outer peripheral column of the highrise building; or in a highrise building having a tube structure or a pure frame structure, the outer peripheral beam which joins to the outer peripheral corner column and is on the first floor level is removed, or the flat slab is used as the above beam; and in a highrise building having a multi-story shear wall, a beam which perpendicularly crosses subsidiary columns at both the ends of the above shear wall and is on the first floor level is removed, or the flat slab is used as the above beam

Assessing the damping properties of coupled wall structural systems

Abstract: In this paper, the global response of the coupled shear wall assemblies will be studied at two different limit states. The primary objective of this investigation is to establish upper and lower bounds on the level of the damping that will be induced in the system due to yield excursions and energy dissipation of the structural members.