Type Of Structural System Research Articles

Vibration Frequencies of Woodframe Residential Construction

Different methods of vibration measurement, such as ambient and forced vibration techniques, have been used in existing woodframe houses to determine fundamental frequency, but because of the highly nonlinear nature of this type of structural system, the reported results vary significantly. This paper discusses some of the differences of frequency values observed in various experimental studies, and identifies the source of these differences by relating the measured fundamental period to the level of shaking. The experimental results from different full-scale tests of woodframe houses and single wood shear walls are used in this paper to gain an improved understanding of the dynamic characteristics of this type of construction and to help explain the differences in results from ambient and forced vibration techniques. A simple equation to estimate forced vibration periods from ambient vibration periods is presented, and its possible application in engineering practice is discussed.

Seismic Performance of RC Coupled Short-Pier Shear Walls with Concealed Bracing

The RC short-pier shear wall structure is a new type of structural system in tall residential buildings. It has been applied in many buildings in China, but its seismic performance is worse than that of normal shear wall structures. Therefore, how to improve its seismic performance becomes a problem which has been paid much attention by engineers. In this paper, the seismic performance of short-pier shear walls with concealed bracing is investigated. An experimental study of four 1:3 scale coupled short-pier shear wall specimens has been carried out, two of which were normal coupled short-pier shear walls, and the other two coupled short-pier shear walls with concealed bracing. Based upon the experimental study, the effects of concealed bracing on the load-carrying capacity, stiffness, ductility, hysteretic behavior, energy dissipation and failure mechanism of shear wall are discussed. It is shown that the seismic performance of short-pier shear walls is greatly improved by concealed bracing. Finally, mechanical models for calculating the load-carrying capacity of the shear wall are proposed, and the theoretical results agree well with those from experiments.

Evaluation of the structural response under seismic actions using non-linear static methods

The paper investigates the degree of accuracy achievable when some non-linear static procedures based on a pushover analysis are used to evaluate the seismic performance. In order to assess the significance of different sources of errors, three types of structural systems are analysed: (i) single-degree-of-freedom (SDOF) systems with different hysteretic behaviour; (ii) shear-type multi-degree-of-freedom (MDOF) systems with elastic–perfect plastic (EPP) shear force–interstorey drift relationships; (iii) a steel moment-resisting frame with rigid joints and EPP moment–curvature relationship. In SDOF systems, the source of approximation comes only from the calibration of the demand spectrum, while in MDOF systems some further errors are introduced by the schematization with an equivalent SDOF system. The non-linear static procedures are compared with rigorous time-history analyses carried out by considering ten generated earthquake ground motions compatible with the Eurocode 8 elastic spectra. It was found that SDOF systems with longer periods satisfy the equal displacement approximation regardless of the hysteretic model, while hysteresis loops with smaller energy dissipated indicate lower response for shorter periods. This is the opposite of what predicted by the ATC-40 capacity spectrum method, which underestimates and overestimates, respectively, the actual response of low- and high-ductility systems. Conversely, the inelastic spectrum method proposed by Vidic, Fajfar and Fischinger leads to the most accurate results for all types of structural systems. The analyses carried out on EPP shear-type frames point out a large concentration of the ductility demand on some storeys. However, such a concentration markedly reduces when some hardening is accounted for. Copyright © 2006 John Wiley & Sons, Ltd.

SEISMIC BIFURCATION FOR RESPONSE-CONTROL OF TALL BUILDING STRUCTURES

The response of a structure to a seismic activity depends on the characteristics of the structural system and the seismic activity. To improve the seismic response of a structural system, it is bifurcated into two subsystems: a flexible one, catering to the primary function/occupancy of the system and a stiff one, taking care of the lateral strength requirements and housing major services of the system. Low stiffness associated with large mass in the flexible subsystem results in shifting of natural periods of the system to zones of low seismic input energy. The difference in lateral stiffness of the two subsystems results in differential response, which is utilized by placing floor-level links between the two subsystems; these links absorb and dissipate a substantial part of seismic input energy leading to a minimal structural distress. Three types of structural systems, viz. conventional system, seismically bifurcated system with rigid links (SBS-RL) and seismically bifurcated system with damping links (SBS-DL), are analyzed for various parameters. The study shows that seismic bifurcation (SB) helps in controlling the seismic response of tall building structures. The study further shows that SB technique is useful in improving seismic performance of conventionally-designed existing structures by way of seismic retrofitting.

Shake table tests on single-storey braced timber frames

Concentrically braced timber frames are often used as lateral load resisting systems in wood buildings where large open spaces are required. For application in high-risk earthquake zones, however, the ductility of the system is a concern, since energy absorption is typically limited to the connection region. In this paper, results are presented from a series of shake table tests conducted on single-storey braced frame models with different connections. Diagonal braces with five different connection types were tested, four of which used bolts as fasteners, while one brace had timber riveted connections. Four of the connections had a matching set with an identical configuration that was previously tested quasi-statically. Findings from the tests are presented along with some comments on the seismic behavior of this type of structural system. It was found that the seismic response of the braced frames is highly influenced by the brace connections. Braced frames with small diameter (slender) bolts and timber rivets showed desirable seismic performance, as they were able to dissipate the highest amount of the seismic input energy. A comparison of the quasi-static and shake table tests revealed slight differences in the load–deformation properties of the brace connections.Key words: braced timber frames, seismic response, connections, timber rivets, bolts, ductility, shake table tests.

Determination of seismic design forces by equivalent static load method

In the proposed 2005 edition of the National Building Code of Canada (NBCC), the seismic hazard will be represented by uniform hazard spectra corresponding to a 2% probability of being exceeded in 50 years. The seismic design base shear for use in an equivalent static load method of design will be obtained from the uniform hazard spectrum for the site corresponding to the first mode period of the building. Because this procedure ignores the effect of higher modes, the base shear so derived must be suitably adjusted. A procedure for deriving the base shear adjustment factors for different types of structural systems is described and the adjustment factor values proposed for the 2005 NBCC are presented. The adjusted base shear will be distributed across the height of the building in accordance with the provisions in the current version of the code. Since the code-specified distribution is primarily based on the first mode vibration shape, it leads to an overestimation of the overturning moments, which should therefore be suitably adjusted. Adjustment factors that must be applied to the overturning moments at the base and across the height are derived for different structural shapes, and the empirical values for use in the 2005 NBCC are presented.Key words: uniform hazard spectrum, seismic design base shear, equivalent static load procedure, higher mode effects, base shear adjustment factors, distribution of base shear, overturning moment adjustment factors.

Review of Structural Analysis of Historic Buildings: Restoration, Preservation, and Adaptive Reuse Applications for Architects and Engineers by J. Stanley Rabun

Structural Analysis of Historic Buildings is a 500 page compilation of technical data, calculation methods, case-study information and historical documentation on the analysis and structural evaluation of historic buildings. The book concentrates primarily on American commercial buildings built during the years from 1820 to 1940, which encompasses a significant portion of the historic building stock in the United States. Rabun provides a comprehensive look at the full range of structural issues related to historic evaluation. This includes information on early building laws and codes, design loads, material strengths, and assessment. Also covered is an analysis and review of all major types of structural systems and assemblies such as walls, columns, bearing walls, foundations, and lateral systems. Rabun has organized the book into six main chapters that make it convenient to research or reference individual components depending on the need of the reader. The chapter titles are very representative of the material discussed and are listed here for the convenience of the reader. • Chapter 1: Assessment Methodology: Material Chronology, Early Building Laws, and Loads • Chapter 2: Foundation Systems of American Historic Buildings • Chapter 3: Historic American Building Systems: Walls and Columns • Chapter 4: Historic American Floor Systems–Beams • Chapter 5: Historic American Roof Systems: Lateral Bracing of Buildings • Chapter 6: The Historic Material Assessment Also included in the book is an extensive bibliography of over 90 publications, many of them historical in their own right. This

矩形平面を持つ陸屋根の構造骨組用風荷重(構造)

The primary purpose of this study is to provide simple formulas for estimating the design wind loads for the structural frames of rectangular flat roofs considering the dynamic response to turbulent wind forces. Two types of structural systems are considered here ; that is, (i) a series of simple beams arranged in parallel, and (ii) a structurally integrated type, which acts like an elastic plate, such as space truss. The characteristics of the first modal force are investigated, using a model of the pressure field on the roof. Based on the results, the gust effect factors for estimating the design wind loads are formulated as a function of the geometric and structural parameters of the roof and the turbulence intensity of approach flow. The formulas are verified by comparing the results on the load effects predicted by the formulas with those computed by using the experimental results for the modal force. The results of this study will be used for updating the specifications of roof wind loads in the AIJ Recommendations for Loads on Buildings.

Development and implementation of the effective force testing method for seismic simulation of large–scale structures

This paper describes the development and experimental implementation of a real–time earthquake simulation test method for large–scale structures. The method, effective force testing (EFT), is based on a transformation of coordinates, in which case the structure is fixed at the base (similar to the set–up for the pseudo–dynamic (PsD) test method); however, in the case of EFT, the method is based on a force–control algorithm rather than a displacement–control algorithm. Effective forces, equivalent to the mass of each storey level multiplied by the ground acceleration, are applied at each respective storey. As such, the EFT forces are known a priori for any ground acceleration record. As opposed to the PsD test method in which the ground displacements to be imposed are affected by the measured structural response as the stiffness changes. As in the case of the PsD test method, the EFT method is suitable for testing any type of structural system that can be idealized as a series of lumped masses (e.g. building or bridge structures). Research has been conducted on a linear elastic single–degree–of–freedom system at the University of Minnesota to develop and investigate implementation of the EFT method. A direct application of the EFT method was found to be ineffective because of a natural velocity feedback phenomenon between the actuator and the structure to which it is attached. A detailed model of the control, hydraulic and structural systems was developed to study the interaction problem and other nonlinear responses in the system. The implementation of an additional feedback loop using the measured velocity of the test structure was shown to be successful at overcoming the problems associated with actuator–ndash;control–ndash;structure interaction, indicating that EFT is a viable real–time method for seismic simulation studies.

Design and Construction Considerations for Continuous Post-Tensioned Bulb-Tee Girder Bridges

Post-tensioned bulb-tee girders provide an extremely cost-effective structural system for bridge construction. Use of high strength concrete and further refinement of the structural system promises to yield longer spans, while providing even greater economy and durability. The analysis, design and construction of a prestressed, post-tensioned bulb-tee girder bridge requires careful consideration of a multitude of factors. This article attempts to outline the essential design and construction considerations for a composite prestressed and post-tensioned system in accordance with the AASHTO LRFD Bridge Design Specifications. The structural system reviewed consists of precast, pretensioned bulb-tee girders, field spliced and post-tensioned in two stages for a continuous composite structural system spanning 3 to 5 spans. This type of structural system has been used extensively and economically for bridges requiring moderately long spans ranging up to 320 ft (97.5 m).

Seismic Performance of Moment-Resisting Steel Frame Structures Designed for Different Levels of Seismic Hazard

A large number of low and medium-rise buildings have moment-resisting steel frames as the primary lateral load resisting system. This type of structural system has been considered to be one of the most effective means for resisting strong seismic ground motions. This paper presents the results of an investigation into the performance which can be expected when code designed ductile moment-resisting steel frame buildings having ductile connections, designed for different seismic hazard levels, are subjected to excitation by strong seismic ground motions. Design variations at different seismic hazard levels include three design philosophies, namely strong-column weak-beam, weak-column strong-beam and strong-column weak panel zone. The analytical model used in the study takes into account both connection flexibility and panel zone shear deformation. Results show that the performance arising from a specific design philosophy may be acceptable in one seismic hazard region, while being unacceptable in a region having a different seismic hazard level.

The Oklahoma City Bombing: Summary and Recommendations for Multihazard Mitigation

From visual inspection and analysis of the damage that occurred in the Murrah Building as a result of a blast caused by a large truck bomb, it is shown that progressive collapse extended the damage beyond that caused directly by the blast. The type of damage that occurred and the resulting collapse of nearly half the building is consistent with what would be expected for an ordinary moment frame building of the type and detailing available in the mid-1970s when subjected to the blast from such a large truck bomb. Using information developed for the Federal Emergency Management Agency and the Department of Housing and Urban Development, types of structural systems that would provide significant increases in toughness to structures subjected to catastrophic loading from events such as major earthquakes and blasts are identified. One of these systems is compartmentalized construction, in which a large percentage of the building has structural walls that are reinforced to provide structural integrity in case ...

DETERMINATION OF LONG TERM DISTRIBUTION OFSTRESS RANGES FOR FATIGUE RELIABILITYANALYSIS OF A TLP DESIGNED FOR CAMPOS BASIN

The tension leg platform (TLP) is a type of structural system for exploitation of oil and gas fields below sea floor and must be designed to avoid fatigue damage due to cyclic action of sea waves. Fatigue is a phenomenon which presents high randomness, making a probabilistic study of major concern. In this work, a methodology to obtain the probability distribution function of time to fatigue failure is applied to a point in the hull and to one tendon of a TLP designed for Campos Basin, offshore Brazil. The short term responses at these points are obtained through a stochastic analysis in frequency domain and Miner's rule is used to assess the fatigue damage. Long term statistics are introduced through a scatter diagram of Campos Basin. Different alternatives of fitting known distributions to the calculated long term distribution of stress ranges are presented. Wirsching's model, assuming only lognormal variates, is compared to more general formats, where the method FORM is employed to assess the probability of failure. Assuming minimum acceptable reliability indices over the service life of the platform, maximum intervals of time to first inspection at referred points are determined.

Site-Dependent Building Response in Singapore to Long-Distance Sumatra Earthquakes

Singapore is a city state located in a low seismicity area with mild winds. The country is a classic example of low seismic hazard and high exposure scenario. It is about 400 km away from a highly active earthquake belt, the Sumatra subduction complex, where great earthquakes have occurred in the past. Twenty-seven earthquakes have been reportedly felt in Singapore since the British settlement in 1819. The frequency of these felt events seems to be rising with time as the country develops. The response of a building to long-distance earthquakes is dependent on the type of structural systems and the local geological conditions. Tall buildings founded on Quaternary deposit, i.e. the Kallang Formation, are particularly apt to respond to the long-distance Sumatra earthquakes. Microtremor measurement results correlate well with the geological conditions and give evidence to the phenomenon of site dependent building response in Singapore to the long-distance Sumatra earthquakes.

ACTIVE AND SEMI‐ACTIVE CONTROL OF STRUCTURES UNDER SEISMIC EXCITATION

Considerable effort has been devoted to develop passive and active methods for reducing structural response under seismic excitations. Passive control approaches have already found application in practice. Active control methods, on the other hand, are being vigorously examined for application to civil structures. This paper investigates the application of active and semi-active control schemes to structures subjected to seismic excitations, and it focuses on the use of the sliding-mode control approach for the development of the control algorithms. The possibility of control redundancy with respect to the number of sliding constraints is taken into account in the controller design. Several sets of numerical results are obtained for a realistic 10-storey shear building, subjected to earthquake-induced ground motions and controlled by active or semi-active control schemes. It is observed that both active and semi-active control schemes can be used to reduce the dynamic response. Active control performs very effectively in reducing the structural response, but the required control force values can be quite large to limit its practical application in the case of large and massive buildings. Active regulation of linear viscous dampers was found unnecessary for this type of structural system, as it did not induce any significantly more reduction in the response than the dampers acting passively. On the other hand, it is shown that active regulation of stiffness can be used with advantage to reduce the response. © 1997 by John Wiley & Sons, Ltd.

EQUIVALENT LINEARIZATION OF GENERALLY PINCHING HYSTERETIC, DEGRADING SYSTEMS

Many types of structural systems that undergo cycles of inelastic deformation under severe natural hazard loadings exhibit 'pinching' of hysteresis loops. In this paper, a generally pinching hysteretic restoring force model-an extension of the Bouc-Wen differential hysteresis model-is used in stochastic equivalent linearization of single-degree-of-freedom structural systems. The severity and rate of pinching are controlled by the hysteretic energy dissipation and the pinching level can be specified to match experimental data. Under white noise excitations, estimates of reponse statistics from linearization are shown to compare favourably with those from Monte Carlo simulation. Numerical studies on the sensitivity of the accuracy of response statistics obtained by linearization to changes in the hysteresis parameters showed that, for a range of practical cases, the linearization method can be used in lieu of simulation and that, in low-frequency systems, some hysteresis parameters may be set to a constant value a priori to reduce the number of model parameters that needs to be estimated or identified, and to simplify further random vibration analysis and/or performance evaluation studies.

EQUIVALENT LINEARIZATION OF GENERALLY PINCHING HYSTERETIC, DEGRADING SYSTEMS

Many types of structural systems that undergo cycles of inelastic deformation under severe natural hazard loadings exhibit ‘pinching’ of hysteresis loops. In this paper, a generally pinching hysteretic restoring force model—an extension of the Bouc–Wen differential hysteresis model—is used in stochastic equivalent linearization of single-degree-of-freedom structural systems. The severity and rate of pinching are controlled by the hysteretic energy dissipation and the pinching level can be specified to match experimental data. Under white noise excitations, estimates of reponse statistics from linearization are shown to compare favourably with those from Monte Carlo simulation. Numerical studies on the sensitivity of the accuracy of response statistics obtained by linearization to changes in the hysteresis parameters showed that, for a range of practical cases, the linearization method can be used in lieu of simulation and that, in low-frequency systems, some hysteresis parameters may be set to a constant value a priori to reduce the number of model parameters that needs to be estimated or identified, and to simplify further random vibration analysis and/or performance evaluation studies.

Optimal structural design via optimality criteria as a nonsmooth mechanics problem

In the theory of plastic structural design via optimality criteria (due to W. Prager), the optimal design problem is transformed to a nonlinear elastic structural analysis problem with appropriate stress-strain laws, which generally include complete vertical branches. In this context, the concept of structural universe (in the sense of G. Rozvany) permits the treatment of complicated optimal layout problems. Recent progress in the field of nonsmooth mechanics makes the solution of structural analysis problems with this kind of “complete” law possible. Elements from the two fields are combined in this paper for the solution of optimal design and layout problems for structures. The optimal layout of plane trusses with various specific cost functions is studied here as a representative problem. The use of convex, continuous and piecewise linear specific cost functions for the structural members leads to problems of linear variational inequalities or equivalently piecewise linear, convex but nonsmooth optimization problems, which are solved by means of an iterative algorithm based on sequential linear programming techniques. Numerical examples illustrate the theory and its applicability to practical engineering structures. Following a parametric investigation of an optimal bridge design, certain aspects of the optimal truss layout problem are discussed, which can be extended to other types of structural systems as well.

A simple method for the determination of the fundamental frequency of vibration of bones

Knowledge of the fundamental frequency of transverse vibrations of bones is of interest in bioengineering applications. The finite method is probably the best tool for the numerical determination of natural frequencies and mode shapes of any type of structural system. The present study proposes a simple approach based on the optimized Rayleigh-Ritz method which yields satisfactory answers for many practical applications.

A Basis for Evaluation of Seismic Hazard and Design Criteria for Saudi Arabia

This paper presents the fundamental issues and policy decisions that formed the basis of the hazard and design aspects of a comprehensive research project conducted for development of the preliminary seismic design criteria for the Kingdom of Saudi Arabia. The study represents the first regionally consistent and systematic collection and critical treatment of the limited historical and instrumental data on earthquakes and seismotectonics of the region, and development of seismic design criteria. The development of the seismic design criteria followed somewhat conservative course, rather than a strict scientific approach, in estimation of the seismic hazard. One of the significant outcome of the study was the preparation of an upto-date and refined earthquake catalog of the region. The catalog contains both, the historical data available in Arabian and English literature, and the data recorded by international and local seismic monitoring agencies. The data were critically treated and superimposed upon the available tectonic information of the Arabian peninsula to obtain a preliminary seismotectonic map of the region. The results of the probabilistic seismic hazard assessment indicate that the highest relative predicted ground-motion occurs near the northwestern border neighboring the Gulf of Aqaba and also near the southwestern border, neighboring Yemen. Based on iso-acceleration map for 10% probability of being exceeded in 50 years, for the seismic design purposes the Kingdom was delineated into four seismic zones. Following UBC format the seismic zones are assigned numbers 0, 1, 2A and 2B. Widely used codes, SEAOC and UBC were selected as the model for development of seismic design recommendations. Selection of the structural system is based on structural performance category which is determined by seismic zone number and the intended occupancy category. Rw-factors for different types of structural system were assigned lower values in consonance with the design and construction practices prevalent in the country. The significance of this study is in its implementation of a global scheme in development of seismic design criteria of a region beset with limited seismic data.