Showing papers in "Journal of Structural Engineering-asce in 1985"

Mechanistic Seismic Damage Model for Reinforced Concrete

Abstract: A model for evaluating structural damage in reinforced concrete structures under earthquake ground motions is proposed. Damage is expressed as a linear function of the maximum deformation and the effect of repeated cyclic loading. Available static (monotonic) and dynamic (cyclic) test data were analyzed to evaluate the statistics of the appropriate parameters of the proposed damage model. The uncertainty in the ultimate structural capacity was also examined.

Seismic Damage Analysis of Reinforced Concrete Buildings

Abstract: Experiences from past strong earthquakes, such as the 1968 Miyakiken-Oki earthquake in Japan and the 1971 San Fernando earthquake in California, have shown the vulnerability of reinforced concrete buildings to strong ground shakings. For economic reasons, however, some level of damage should be expected and permitted in the aseismic design of structures, particularly of low-rise buildings. In spite of this recognition, the potential seismic damage of structures and the associated aseismic provisions are based largely on qualitative engineering judgment. In order to assess the seismic safety of reinforced concrete buildings, the quantitative analysis of structural damage under random earthquake excitations needs to be improved.

Friction coefficient of steel on concrete or grout.

Abstract: An experimental investigation was conducted to determine the coefficient of static friction between rolled steel plate and cast‐in‐place concrete or grout. Fifteen tests were performed under conditions that represented the interior and exterior bearing surfaces of a containment vessel. Test parameters included concrete blocks or grout blocks, wet or dry interface, and level of normal compressive stress. For conditions tested, the average effective coefficient of static friction varied between 0.57 and 0.70. It is recommended that the coefficient of static friction for concrete cast on steel plate and grout cast below steel plate should be taken as 0.65 for a wet interface with normal compressive stress levels between 20 and 100 psi (0.14 and 0.6 MPa). For dry interface, the coefficient of static friction should be taken as 0.57.

Pseudodynamic Method for Seismic Testing

Abstract: The pseudodynamic method is a relatively new experimental technique for evaluating the seismic performance of structural models in a laboratory by means of on-line computer controlled testing. During such a test, the displacement response of a structure to a specified dynamic excitation is numerically computed and quasi-statically imposed on the structure, based on analytically prescribed inertia and viscous damping characteristics for the structure and the experimentally measured structural restoring forces. This paper presents the basic approach of the method, describing the numerical and experimental techniques. Based on current studies, the capabilities and limitations of the method are examined, and possible improvement methods are mentioned. In spite of certain numerical and experimental errors, recent verification tests show that the method can be as reliable and realistic as shaking table testing and that it can be readily implemented in many structural laboratories. The capabilities of the method can be further expanded to test specimens under various load and structural boundary conditions.

Simplified Earthquake Analysis of Structures with Foundation Uplift

Abstract: Simplified analysis procedures are developed to consider the beneficial effects of foundation‐mat uplift in computing the earthquake response of structures, which respond essentially as single‐degree‐of‐freedom systems in their fixed‐base condition. These analysis procedures are presented for structures attached to a rigid foundation mat, which is supported on rigid foundation soil or flexible foundation soil modeled as two spring‐damper elements. Winkler foundation with distributed spring‐damper elements, or a viscoelastic half‐space. In these analysis procedures, the maximum earthquake‐induced base shear and deformation for an uplifting structure are computed directly from the earthquake response spectrum. It is demonstrated that the simplified analysis procedures provide results for the maximum base shear and deformation to a useful degree of accuracy for practical structural design.

Mechanics of Masonry in Compression

Abstract: Strength and deformation of clayunit masonry under uniaxial concentric compressive force were investigated. Biaxial tensioncompression tests of bricks and triaxial compression tests of mortar were ...

Distortional Buckling of Steel Storage Rack Columns

Abstract: A distortional mode of buckling is described for cold-formed lipped channel columns that have additional flanges attached to the flange stiffening lips. The purpose of the additional flanges, called “rear flanges,” is to permit bolting of braces to the channel section so as to form upright frames of steel storage racks. Theoretical and experimental evidence of this mode of buckling is provided for perforated and unperforated columns. A set of design charts is included to permit calculation of the distortional buckling stresses of a range of sizes of practical channel sections with rear flanges.

Lateral‐Torsional Motion of Tall Buildings to Wind Loads

Abstract: The lateral‐torsional motion of tall buildings is investigated. For a square cross‐section building, expressions for the alongwind, acrosswind and torsional loading are developed through the use of spatio‐temporal fluctuations in the pressure field around the building. A simplified formulation is used to represent the dynamic behavior of torsionally coupled buildings by considering a class of buildings in which all floors have the same geometry in plan, the eccentricities between the elastic and mass centers are the same for all stories, and the ratio of the story stiffness in lateral directions is about the same for all stories. Methods of random vibration theory are used to estimate the rms and peak values of various components of response. The results indicate that the torsional response contributes significantly towards the overall dynamic response of a symmetric building. Inclusion of coupling between the lateral and torsional degrees‐of‐freedom further increases the building response. The procedure ...

Structural Optimization Using Reliability Concepts

Abstract: An overview of the major concepts and methods used in reliabilitybased structural optimization is presented. New formulations related to multicriteria optimization are developed. Comparative results are presented when different criteria are used for the optimum design of a structure under service and ultimate reliability constraints. It is concluded that reliability‐based optimization is now practicable for structural engineers. The writing of appropriate reliability‐based optimum design software is a vital element at present receiving too little attention.

Seismic Response of Light Subsystems on Inelastic Structures

Abstract: Preliminary analyses are performed to obtain insight into the seismic response of light, acceleration sensitive nonstructural subsystems supported on structures that yield during severe earthquake ground motions. The effects of the severity of the inelastic deformations, of different hysteretic characteristics of the structure and of the amount of viscous damping of the subsystem are thoroughly investigated. Current design recommendations for subsystems accounting for yielding of the supporting structure are assessed and found to be unconservative. An amplification factor is defined to quantify the effects of inelastic deformations of the supporting structure on subsystem response. Design guidelines are formulated for predicting the amplification factor based on statistical evaluation of the results generated for ten earthquake ground motions. Using these values, design floor response spectrums can be obtained from conventional linear elastic floor response spectrums accounting for yielding of the support...

Racking Deformations in Wood Shear Walls

Abstract: The theory presented in this paper predicts racking deformations in wood‐stud shear walls. The energy method employed defines the wall performance in terms of the lateral nonlinear load‐slip behavior of the nails which fasten the sheathing to the frame. Using power curves to define the nail loadslip relationship, the theory predicts that wall deformation due to nail slip will also be defined by a power curve. The theory also includes linear deformation due to shear distortion of the sheathing material, and provides accurate estimation of wall performance up to moderate load levels. The method presented should be of interest to engineers who design light frame structures, to researchers, and to those who are concerned with building codes.

Hysteretic dampers in base isolation: Random approach

Abstract: A method of random vibration analysis of base isolated structures with hysteretic dampers is employed. The hysteretic restoring force is modelled by a nonlinear differential equation. The equations of motion for shear type structures are linearized in closed form. Nonstationary response statistics for evolutionary nonwhite excitation are determined by solving the associated Lyapunov matrix differential equation. An optimization study which is based on the stationary response is also presented.

Cyclic Out-of-Plane Buckling of Double-Angle Bracing

Abstract: The behavior of double‐angle bracing members subjected to out‐of plane buckling due to severe cyclic load reversals is investigated. Nine full‐size test specimens were subjected to severe inelastic axial deformations. Test specimens were subjected to severe inelastic axial deformations. Test specimens were made of back‐to‐back A36 steel angle sections connected to the end gusset plates by fillet welds or high‐strength bolts. Five of the test specimens were designed according to current design procedures and code requirements. These specimens experienced fracture in gusset plates and stitches during early cycles of loading. Based on the observations and analysis of the behavior of these specimens, new design procedures are proposed for improved ductility and energy dissipation capacity of double‐angle bracing members which buckle out of plane of gusset plates. Tests of four specimens, designed using proposed procedures, showed significant improvement in their performances.

Behavior of Wood‐Framed Shear Walls

Abstract: Shear walls play an important role in the wind and seismic resistance of lowrise woodframed buildings. The behavior of shear walls is primarily governed by the nail forceslip characteristics. The b...

Laminated Glass Units under Uniform Lateral Pressure

Abstract: Laminated flat glass is gaining popularity as an architectural glazing product. Despite its increased use as a cladding material, its structural properties are not well known. Research undertaken to advance understanding of the behavior of laminated glass units under lateral pressure representing wind loads is reported. Laminated glass units are comprised of two layers of glass connected by a thin interlayer of polyvinyl butyral. The material properties of the interlayer are very different from the properties of the glass plates which it joins together; its modulus of elasticity in shear is only about 1/10,000th that of glass. Experimental stress analyses were conducted on several laminated glass units to ascertain whether their behavior was similar to a monolithic glass plate of the same nominal thickness, or to a layered glass unit consisting of two glass plates with no interlayer. At room temperature the laminated glass unit behaves much like a monolithic glass plate of the same nominal thickness. At elevated temperatures [170°F (77°C)] the behavior changes, and approaches that of a layered glass unit with no interlayer. Results of the experimental stress analyses are compared with theoretical stress analyses designed to characterize the behavior of monolithic glass plates and layered glass units.

Analysis of Events in Recent Structural Failures

Abstract: A study of nearly 150 recent major collapses and distresses of structures around the world discloses that external events and deficiencies in the areas of construction and design were the principal sources of failures. More than one-third of the surveyed structures were bridges, and the remaining were low-rise, multi-story, plant-industrial, and long-span buildings. The major incidents in the category of external events were the lateral impact forces and other unexpected live loads on bridges, and explosion impact loads in concrete silos. Construction deficiencies included falsework and concreting faults in several concrete structures and inadequate welding operations in steel bridges. Design deficiency related events were found to vary with the type of the observed structures, but a significant number of failures were attributed to lack of knowledge in long-term creep and shrinkage effects on prestressed concrete members. These findings suggest that attention should be directed to three areas: (1) Identification of potential deficiencies from past failure data; (2) enhancement in procedural methods during design and construction operations; and (3) incorporation of risk analyses of structures during their service life and construction phases.

Random creep and shrinkage in structures: Sampling

Abstract: This paper deals with uncertainty in the prediction of the effects of creep and shrinkage in structures, such as deflections or stresses, caused by uncertainties in the material parameters for creep and shrinkage, including the effect of random environmental humidity. This problem was previously analyzed using two‐point estimates of probability moments. Here the same problem is analyzed using latin hypercube sampling. This has the merit that the number of required deterministic structural creep analyses is reduced from 2n to approximately 2n, where n=numberofrandomparameters. A method of taking into account the uncertainty due to the error of the principle of superposition is also presented. The mean and variance of creep effects in structures are calculated and scatter bands are plotted for seven typical practical examples, and the results are found to be close to those obtained with two‐point estimates. Further, it is demonstrated that the distribution of creep effects is approximately normal if the cre...

Simplified Earthquake Analysis of Multistory Structures With Foundation Uplift

Abstract: A simplified analysis procedure is developed to consider the beneficial effects of foundation‐mat uplift in computing the earthquake response of multistory structures. This analysis procedure is presented for structures attached to a rigid foundation mat which is supported on flexible foundation soil modeled as two spring‐damper elements, Winkler foundation with distributed spring‐damper elements, or a viscoelastic half space. In this analysis procedure, the maximum, earthquake induced forces and deformations for an uplifting structure are computed from the earthquake response spectrum without the need for nonlinear response history analysis. It is demonstrated that the maxr imum response is estimated by the simplified analysis procedure to a useful degree of accuracy for practical structural design.

Biaxial Stress‐strain Relations for Brick Masonry

Abstract: Simple nonlinear stress‐strain relations for brick masonry constructed with solid pressed bricks are derived from the results of a large number of biaxial tests on square panels with various angles of the bed joint to the principal stress axes. The macroscopic elastic and nonlinear stress‐strain relations are determined from, displacement measurements over gage lengths which included a number of mortar joints. Although the initial elastic behavior is found to be close, on average, to isotropic, the nonlinear behavior is strongly influenced by joint deformations and is best expressed in terms of stresses and strains referred to axes normal and parallel to the bed joint. A given strain is related only to the corresponding stress by a power law, except when the ratio of the shear to normal stress on a bed joint is greater than 1. In the latter case, a bilinear relation is more appropriate. Dependence on other stress components is masked by the variability in the results.

Vibration of Tapered Beams

Abstract: Stiffness and consistent mass matrices for linearly tapered beam element of any cross‐sectional shape are derived in explicit form Exact expressions for the required displacement functions are used in the derivation of the matrices Variation of area and moment of inertia of the cross section along the axis of the element is exactly represented by simple functions involving shape factors Numerical results of vibration of some tapered beams are obtained using the derived matrices and compared with the analytical solutions and the solutions based upon stepped representation of the beams using uniform beam elements The significance of the severity of taper within beams upon solution accuracy and convergence characteristics is examined

Sensitivity of Reliability‐Based Optimum Design

Abstract: A reliability‐based optimization sensitivity analysis technique based on the feasible directions concept is presented for plastic design of redundant structures. This technique is specialized to a formulation of the problem of plastic optimization for minimum weight based on a rational reliability constraint for sizing members. The technique is demonstrated with a structural design example where emphasis is placed on the sensitivity of the reliability‐based optimum solution to both the correlation among strengths and the method for evaluating the overall probability of plastic collapse.

Constitutive Model for Dynamic Loading of Concrete

Abstract: Constitutive properties of concrete under dynamic loading are necessary for the rational analysis of concrete structures subject to impact and impulsive loads. The constitutive model presented herein models microcracking through the use of a continuous damage parameter for which a vectorial representation is adopted. The rate of increase of the damage is dependent on the state of strain as well as on the time rate of strain. The constitutive equations are derived from the strain energy function which is influenced by the accumulated damage. The constitutive model is calibrated using uniaxial tension (or flexural) and uniaxial compression test data. The calibrated model is then used to predict certain other load responses of concrete.

Biaxially Loaded L‐shaped Reinforced Concrete Columns

Abstract: Results of an experimental and analytical investigation on the strength and deformation of biaxially loaded short and tied columns with L‐shaped cross section are presented. The study explores the behavior of reinforced concrete columns under loads monotonically up to failure. A few tests loaded cyclically are also compared with those loaded monotonically. The strength interaction curves and load contours of L‐shaped columns based on analysis and some test results are shown in this paper to provide advice for design information. Two design examples are given to provide possible design procedures.

Impact studies on small composite girder bridge

Abstract: Two impact studies on a small-span, composite girder highway bridge have given widely scattered impact fractions, with a maximum of 1.32 as compared with the AASHTO code value of 0.30 for this bridge. Field strains were used to measure maximum mid-span bending moments for 170 trucks in normal traffic, and these were compared with equivalent static values computed from axle weights measured by a weighbridge. Impact fractions varied from - 0.08 to + 1.32 for gross vehicle weights from 27 - 44 ton. Large impact values occurred for both light and heavy vehicles and were repeated in two independent series of tests. The scatter of the results suggests that impact is vehicle dependent, and that it may vary with suspension geometry. Possible causes of high impact are discussed. (Author/TRRL)

Tests of Full‐Size Gusset Plate Connections

Abstract: The paper presents an evaluation of the behavior and strength of gusset plates on the basis of an experimental investigation of full‐scale diagonal bracing connections. Sugh connections commonly occur in heavy industrial structures, for example. The evaluations are based on analyses of load and deformation data that were generated during the tests, including the failure patterns for the plates. A total of six tests were run, using three bracing member orientation angles. The results are correlated with analytical studies, with special emphasis on recent finite element work. The results are found to be in reasonable agreement Current design practices are discussed briefly; some of the methods are shown to be in acceptable agreement with the tests. It is shown that plate boundaries, plate buckling, and related out‐of‐plane bending phenomena have significant effects on the plate behavior. Recommendations for additional work are also made.

Stochastic Evaluation of Seismic Structural Performance

Abstract: A method is presented for determining the probabilities of a structure sustaining various levels of damage due to seismic activity during its lifetime. Uncertainties in the loading and the structural response analysis are considered. The method is based on a nonlinear random vibration analysis and an analytical technique for evaluating the sensitivity of the response to various structural and load parameters. Recently reported data are used to update the parameter values commonly used in the random process representation of earthquakes. The method is illustrated by analyses of a four‐story steel frame building and a seven‐story reinforced concrete building.

Wind Induced Lateral‐Torsional Motion of Buildings

Abstract: Fluctuating wind forces on tall buildings can cause excessive building motion that may be disturbing to the occupants. A method to relate dynamic alongwind, acrosswind, and torsional forces acting on square isolated buildings to building accelerations is developed using random vibration theory. Wind tunnel test data are analyzed to determine the spectra of force components and correlations among the different components of force. The effects on building vibration of statistical correlations among components of force and mechanical coupling of components of motion introduced by eccentricities of the centers of mass and rigidity from the building centroid are examined. Comparison are made with more common building analyses, where the forces are assumed to be statistically uncorrelated and the components of motion are assumed to be uncoupled.

Nonuniform Bending‐Stress Distribution (Shear Lag)

Abstract: Nonuniform normal longitudinal stress distribution in a trapezoidal box beam with lateral cantilever is discussed. The problem is solved by the variational method assuming as unknown the displacement of the beam axis and three functions which describe the warping of the horizontal flanges; the unknowns are reduced in case of vertical walls. The state of stress of stress in each structural element is analyzed and an example is given to illustrate the results.

I Interaction of Plastic Local and Lateral Buckling

Abstract: Attention is given to the interaction between local and lateral buckling of I‐sections and their influence on plastic flexural ductility in regions of moment gradient. It is shown by means of simple theoretical formulations and the results of a series of tests to failure that rotation capacity in the plastic range is influenced significantly not only by conventional codified parameters, but also by the ratio of span to flange thickness and coincident axial force. In addition, the interaction between local and lateral buckling in the plastic region is demonstrated, and a model is formulated for quantifying this strain‐weakening effect. The results are relevant to the plastic design of structures as well as more general research into methods of improving flexural ductility of I‐sections.

Construction Load Analysis for Concrete Structures

Abstract: A common practice in multistory reinforced concrete building construction is to shore a freshly placed concrete floor on several previously cast floors. The construction loads on the supporting floors may exceed the slab design loads during maturity, especially when the design live load is small compared with the dead load. A few studies have been conducted to analytically model the construction loading process. However, these early models are based on a number of simplifying assumptions. The objective of this paper is to develop a three‐dimensional computer model which can be used to evaluate the effect of variations of the foundation rigidity, column axial stiffness, slab aspect ratio, and shore stiffness distribution on the values of the shore loads and slab moments.