Search

Reports that the American Society of Civil Engineers (ASCE) and the Structural Engineering Institute (SEI) are looking for nominations for the 2006 ASCE and SEI Awards. Objective of the ASCE and SEI Honors and Awards Programs; ASCE awards based on meritorious papers; SEI awards.

The traditional approach to formulating building codes often is slow and labor-intensive, and may struggle to keep pace with the rapid evolution of technology and domain findings. Overcoming such challenges necessitates a methodology that streamlines the modernization of codal provisions. This paper proposes a machine learning (ML) approach to append a variety of codal provisions, including those of empirical, statistical, and theoretical natures. In this approach, a codal provision (i.e., equation) is analyzed to trace its properties (e.g., engineering intuition and causal logic). Then a ML model is tailored to preserve the same properties and satisfy a collection of similarity and performance measures until declared equivalent to the provision at hand. The resulting ML model harnesses the predictive capabilities of ML while arriving at predictions similar to the codal provision used to train the ML model, and hence it becomes possible to use in lieu of the codal expression. This approach was examined successfully for seven structural engineering phenomena contained within various building codes, including those in North America and Australia. The findings suggest that the proposed approach could lay the groundwork for implementing ML in the development of future building codes. [ABSTRACT FROM AUTHOR]

Introduces the August 2005 issue of the "Journal of Structural Engineering". Special theme section of the papers that deal with various research aspects related to a structure's response to blast and impact loads; Article on whether seismic design provisions can improve the resistance of buildings to blast loads and progressive collapse; Integration scheme that makes use of higher-order polynomial approximations.

Presents an introduction to various articles published in the January 2005 issue of the "Journal of Structural Engineering."

As inelastic design for wind is embraced by the engineering community, there is an increasing demand for computational tools that enable the investigation of the nonlinear behavior of wind-excited structures and subsequent development of performance criteria. To address this need, a probabilistic collapse assessment framework for steel structures is proposed in this paper. The framework is based on the integration of a high-fidelity fiber-based nonlinear structural modeling environment with a wind-tunnel-informed stochastic wind load model to perform nonlinear time history analysis. General uncertainty is propagated using a stratified sampling scheme enabling the efficient estimation of reliabilities associated with rare events. The adopted models for simulating high-fidelity nonlinear structural behavior were found, in general, to be adequate for capturing phenomena, including progressive yielding, buckling, and low-cycle fatigue, that are essential for wind induced collapse analysis. In particular, the adopted fatigue model was found to be capable of predicting damage and potential fiber/section fracture associated with non–fully reversing stress-strain cycles that are characteristic of wind loading. Through illustration on a 45-story archetype steel building, critical discussions on the types of observed collapse mechanisms, the difference between along-wind and across-wind nonlinear behavior, reliabilities associated with first yield, and collapse are presented. A probabilistic description of the residual and peak story drifts is also provided through development of fragility functions. [ABSTRACT FROM AUTHOR]

Focuses on the American Society of Civil Engineers and Systems Engineering and Integration awards. Objective of the awards; Categories of the awards.

Funicular geometries, which follow the idealized shapes of hanging chains under a given loading, are recognized as materially efficient structural solutions because they exhibit no bending under design loading, usually self-weight. However, there are circumstances in which nonstructural conditions make a funicular geometry difficult or impossible. This paper presents a new design philosophy, based on graphic statics, that shows how bending moments in a nonfunicular two-dimensional curved geometry can be eliminated by adding forces through an external posttensioning system. An interactive parametric tool is introduced for finding the layout of a posttensioning tendon for any structural geometry. The effectiveness of this approach is shown with several new design proposals. [ABSTRACT FROM AUTHOR]

Link-to-column connections in steel eccentrically braced frames must be capable of sustaining large cyclic forces and inelastic rotations. United States code provisions require that satisfactory performance of link-to-column connections be verified by testing under a prescribed loading protocol. However, there are few link-to-column connection details that have satisfied these testing criteria. This paper describes a pilot investigation of two promising link-to-column connection details, as follows: (1) the fillet welded connection, which uses fillet welds or a combination of fillet and groove welds between the link and the column flange; and (2) the supplemental web doubler connection, which reinforces the connection region using a pair of doubler plates in the first link web panel next to the column, parallel to but offset from the link web. These two details showed excellent performance in a series of eight tests. This paper describes these link-tocolumn connection details, summarizes the results of cyclic loading tests, and discusses design issues and approaches for these connections. [ABSTRACT FROM AUTHOR]

The redundancy of a structure refers to the extent of degradation the structure can suffer without losing some specified elements of its functionality. However, because future structural degradation is unknown during design and analysis, it is evident that structural redundancy is related to robustness against uncertainty. This paper proposes a quantitative and widely applicable concept of strong redundancy and shows its relation to the info-gap robustness of the structure. In particular, one of this paper's propositions establishes general conditions in which the strong redundancy is equivalent to the robustness. This paper also defines a concept of weak redundancy and presents propositions that relate it to the strong redundancy and the robustness. Results are illustrated with several heuristic and engineering examples. [ABSTRACT FROM AUTHOR]

Probabilistic techniques are of vital use in predicting the seismic story drifts of buildings, which vary due to uncertainties in the characteristics of future earthquake motions. This paper proposes a procedure for evaluating the expected mean and standard deviation of seismic story drifts of reinforced concrete buildings by considering both total and story failure mechanisms. The estimation process consists of a pushover analysis of the structure against inverted triangular forces to evaluate the most probable mechanism during earthquakes, followed by consideration of the relative reserve strengths to evaluate the probability of other mechanisms. The relative reserve strengths against story and total mechanisms are expressed by two newly defined story-safety and total-reduction factors, respectively. In this paper, the proposed procedure is verified by conducting dynamic response analyses of 9-story wall and frame structures with various story-safety and total-reduction factors using 36 records from 14 different earthquakes. The proposed procedure well predicted the mean and standard deviation of story drifts of the structures. Application to wall-frame structures is also discussed. [ABSTRACT FROM AUTHOR]

This paper extends the Rankine method to the analyses of reinforced concrete filled steel (RCFS) columns and plain concrete filled steel (PCFS) columns at elevated temperature. The advantage of this approach is that it gives structural engineers a physical feel of the adequacy of a column in terms of its plastic squashing capacity and elastic buckling capacity. The method hinges on the concept of modified buckling coefficient, which is equally applicable for both axially and eccentrically loaded columns. A novel feature is that the fire resistance of a column is expressed in terms of its plastic squashing capacity and elastic buckling capacity at ambient temperature. The mean of agreement between the Rankine predictions and test results for both RCFS (61 columns) and PCFS (95 columns) is satisfactory. The paper includes a worked example to illustrate the flexibility of the approach, and also comments on the accuracy when the Rankine method is applied to other types of columns such as steel or reinforced concrete columns. [ABSTRACT FROM AUTHOR]

Ronald Hamburger The writers thank the discusser for his interest in the paper as well as his comments. However, as discussed in Suzuki and Lignos ([23]; [21]), in large-magnitude earthquakes that exhibit long-duration characteristics [Fig. Beam-column element model calibrated for predicting flexural response leading to global collapse of RC frame buildings. [Extracted from the article]

The article provides closure to the discussion of a research on the topic of equivalent seismic force distribution for design of moment-resisting frames. The authors of the study indicate that the basic premise of the paper is that a lateral stiffness is given. The iterative procedure to achieve the target story ductility levels is clarified.

Introduces a series of articles on structural engineering.

This paper presents the findings of an investigation on the flexural performance of hollow steel pipe piles subjected to reversed cyclic loading. The testing evaluated both spirally double submerged arc welded (DSAW) and traditional longitudinal single seam electric resistance welded (ERW) pipe piles to determine the effects of the spiral welding manufacturing process on the structural performance of the pile. Some of the tests were conducted on previously driven piles to study the effects of driving stresses. The experimental results and observations indicated that the undesirable failure mode of spiral weld cracking did not control the ultimate limit state in any of the spirally welded specimens considered. Although weld fracture did occur in each spirally welded specimen, it did not develop until the specimen was subjected to large inelastic deformations and was ultimately the result of locally increased strains caused by local buckling. Each traditional single seam specimen failed in a similar manner with pile wall local buckling developing at inelastic deformation levels comparable to those of the spirally welded specimens. [ABSTRACT FROM AUTHOR]

Characterization of constructed civil-engineering systems through structural identification (St-Id) has gained increasing attention in recent years due to its potential to enable more effective infrastructure asset management and performance-based engineering. Although there have been recent advances that mitigate the challenges posed by aleatory (random) uncertainty, there are many remaining challenges associated with epistemic (bias) uncertainty that often have a more critical impact on the reliability of St-Id (especially with applications to constructed systems). The objective of this paper is to illustrate various sources of epistemic uncertainty and describe mitigation approaches by detailing the St-Id of a long-span steel arch bridge. This application includes a priori modeling, ambient vibration monitoring, data processing, feature extraction, and finite-element (FE) model correlation. Following a description of the St-Id, the impact of various modeling uncertainties on the calibrated FE model is evaluated by comparing different identification scenarios. Finally, a simple and rational approach to 'truth testing' the identified model is developed and employed to determine its admissibility. [ABSTRACT FROM AUTHOR]

This paper presents analytical estimates of the behavior exhibited by curved, archlike structures under radially directed and gravitational line loads. The behavior is shown to range from elementary beam bending at one end to a state of pure compression at the other, and its behavior can be tracked by an arch rise parameter that is a function of the arch's semivertex angle, radius and thickness. The principal results are useful estimates of the dependence of the major displacements and stress resultants on the arch rise parameter. The results also offer some insight into the assumptions underlying Robert Maillart's arch designs. [ABSTRACT FROM AUTHOR]

Ductile end cross frames have been proposed in the past for seismic design of steel plate girder bridges. In this paper buckling-restrained braces (BRBs) are investigated as ductile end cross frames and compared against the performance of yielding X braces. Component experiments on the BRBs showed that these braces dissipated energy very efficiently and have stable hysteretic behavior. Shake-table experiments on a large scale bridge model investigated the performance of braces with both pin-ended connections and fixed-end connections. Despite slippage, the pin-ended connections are considered more effective as flexural action in the relatively short braces is prevented. The base shear in the bridge model in response to 2.0 times the El Centro earthquake was 69% of the elastic base shear at an average drift of 2.5% during experiments. The relatively large deformation capacity of the BRBs, although not as great as the X braces, is necessary to achieve a significant reduction in base shear. The maximum cross frame displacements with the BRBs are consistently smaller than those in X braces at the same level of base shear. [ABSTRACT FROM AUTHOR]

For assessing the integrity of damaged hollow section joints, the plastic collapse loads of the joints containing cracks is an important parameter. Very little published information is available in the literature concerning the residual strength of square hollow section (SHS) joints containing defects or cracks. In this paper, an accurate numerical modeling of SHS T joints with cracks is proposed, whereby the entire finite element mesh is generated automatically. To validate this numerical model, several T joint models are studied and compared with the experimental data. A good agreement is obtained on the ultimate loads. Based on this model, the plastic collapse loads under different geometrical ratios are studied, and they are compared with the results calculated from the yield line theory. It is found that the yield line theory can give a reasonable prediction of the plastic collapse loads when the brace width to chord width ratio β is less than 0.8. The failure assessment diagrams (FAD), constructed using the J-integral predictions, have confirmed that the standard BS7910 Level 2A FAD is appropriate for determining limits of safe loading of cracked SHS T joints, provided the plastic collapse load is calculated using the yield line formulae neglecting the influence of the welds. [ABSTRACT FROM AUTHOR]

This paper is concerned with the application of the direct strength method to equal angle section beam-columns with locally unstable legs. In contrast to existing design methods, which independently determine the compression and bending capacities and use an interaction equation to combine these, the direct strength method determines the elastic local buckling stress for the actual stress distribution resulting from the combined action of compression and bending, and incorporates the elastic buckling stress into a direct strength equation for beam-columns. In applying the method to equal leg angles, the torsional buckling mode is ignored when determining the overall buckling capacities, since it is accounted for through the local buckling mode, and the shift of the effective centroid is incorporated as an additional loading eccentricity. The shift in the effective centroid resulting from local buckling is determined from the actual stress distribution, as obtained using Stowell’s classical solution, in place of an effective cross section. The predicted strengths are conservative compared to tests on slender equal angle columns, and are shown to accurately predict the variation in load with applied loading eccentricity. [ABSTRACT FROM AUTHOR]

Performance-based engineering concepts applied to both structural design and assessment have gained interest among structural engineers and researchers in recent years. Performance-based design applied to building systems includes selection of appropriate structural systems and configurations to ensure that the structure has adequate strength, stiffness, and energy dissipation capacity to respond to loadings, including those arising from natural hazards, without exceeding permissible damage states. Although performance-based design has advanced for some materials and structural types, such as steel and reinforced concrete buildings and bridges built in high seismic regions, the application to light-frame wood structures has only recently been explored. This paper investigates the application of fragility techniques to the seismic design of engineered woodframe shearwalls. The methodology developed herein provides a technical basis for the development of future performance-based design provisions for shearwalls in light-frame structures subject to earthquake loading. In the present study, shearwalls are treated as isolated subassemblies. Nonlinear dynamic time-history analysis is used to predict the performance of the shearwalls considering a suite of suitably scaled characteristic ordinary ground motions taken to represent the seismic hazard. Examples of fragility curves are developed considering peak wall displacement and ultimate uplift force at the hold-down. The effects of nailing schedule, seismic weight, and choice of response modification factor (R) are considered. [ABSTRACT FROM AUTHOR]

Assessing the structural response and vulnerability of bridge piers to collisions by barges typically involves either the use of static pier analysis codes and design-specification-stipulated equivalent static loading conditions, or a lengthy model development process followed by use of general-purpose finite-element codes. In this paper, an alternative approach is proposed that leverages the capabilities of existing nonlinear dynamic pier analysis programs by adding dynamic barge behavior in a computationally efficient and modular manner. By coupling nonlinear barge and pier responses together through a shared collision impact force and employing numerical procedures for accelerating convergence of the coupled system, dynamic barge collision analyses may be conducted for bridge piers efficiently and rapidly. The influence of impact parameters such as barge type and mass, impact speed and angle, and pier configuration can then be efficiently evaluated using dynamic collision analyses. For demonstration purposes, the method is implemented in an existing pier analysis program, validated, and used to conduct selected case studies. [ABSTRACT FROM AUTHOR]

During the last 3 decades interest has grown globally in the application of ductile steel plate walls (DSPWs) (or steel plate shear walls) for building lateral load resistance. The supporting theory has evolved from both analytical and experimental research conducted in several countries around the world. The advantages of using DSPWs as the lateral force resisting system in buildings include stable hysteretic characteristics, high plastic energy absorption capacity, and enhanced stiffness, strength and ductility. A significant number of experimental and analytical studies have been carried out to establish analysis and design methods for such lateral resisting systems. Despite these efforts there is still a need for a general analysis and design methodology that not only accounts for the interaction of the plates and the framing system but also can be used to better understand the linear and nonlinear behavior of different DSPW configurations. These configurations include DSPWs with thin or thick steel plates, and with or without stiffeners and openings. In this paper an analytical model of the DSPW that responds to this need and characterizes the structural behavior of these configurations is presented and discussed. The proposed model provides a good understanding of how the different components of the system interact, and is able to properly represent the system’s overall hysteretic characteristics, which can be readily incorporated in practical nonlinear analyses of buildings with DSPWs. The effectiveness of the method is demonstrated by comparing the predicted response with results from experimental studies performed by different researchers. [ABSTRACT FROM AUTHOR]

Establishing the strength requirements for stability bracing generally requires large displacement analyses on imperfect systems. In computational studies on stability bracing, choosing the critical shape of the imperfection can be a difficult decision, particularly for beam bracing systems. There are a number of factors that affect the stability brace forces including the shape and magnitude of the imperfection, the distribution of the imperfection along the length, and the value of the moment at the location of the brace. To develop suitable bracing design provisions, it is necessary to determine the maximum brace forces that are likely to occur in typical applications. However, determining the shape and distribution of the imperfection that produces the largest brace forces can be complicated. This paper studies the effect of different imperfection schemes on the magnitude of the stability brace forces. Results are presented that demonstrate the impact of several imperfection parameters on the bracing behavior and recommendations are made for selecting the critical imperfection shape that maximizes the stability brace forces for beam bracing systems. [ABSTRACT FROM AUTHOR]

Safe and economical design and assessment of reinforced (RC) and prestressed concrete (PC) beams requires the availability of accurate but simple formulations which adequately capture the structural response. In this paper, a mechanical model for the prediction of the shear-flexural strength of PC and RC members with rectangular, I, or T sections, with and without shear reinforcement, is presented. The model is based on the principles of concrete mechanics and on assumptions supported by the observed experimental behavior and by the results of refined numerical models. Compact, simple, and accurate expressions are derived for design and verification of the shear strength, which incorporate the most relevant shear transfer actions. Excellent agreement between the predictions of the model and the results of the recently published ACI-DAfStb databases, including more than 1,287 tests on RC and PC beams with and without stirrups, has been observed. The theory behind the model provides consistent explanations for many aspects related to the shear response that are not clearly explained by current code formulations, making it a very helpful tool for daily engineering practice. [ABSTRACT FROM AUTHOR]

In recent years, the concept of resilience has been introduced to the engineering field in particular related to disaster mitigation and management. However, the built environment is only part of the elements that support community functions. Maintaining community functionality during and after a disaster, defined as resilience, is influenced by multiple components. The paper is proposing a framework for measuring community resilience at different spatial and temporal scales. Seven dimensions are identified for measuring community resilience: population and demographics, environmental and ecosystem, organized governmental services, physical infrastructures, lifestyle and community competence, economic development, and social-cultural capital. They are summarized with the acronym PEOPLES. Each dimension is characterized by a corresponding performance metric that is combined with the other dimensions using a multilayered approach. Therefore, once a hybrid model of the community is defined, the proposed framework can be applied to measure its performance against any type of extreme event during emergency and in long term postdisaster phases. A resilience index can be determined to reflect all, or part, of the dimensions influencing the events. Several applications of part of such framework can already be found in literature for different types of infrastructures, physical and organizational (e.g., gas network, water distribution networks, health care facilities). The proposed framework can be used as decision support by stakeholders and managers and it can help planners in selecting the optimal restoration strategies that enhance the community resilience index. [ABSTRACT FROM AUTHOR]

The analysis of wind actions and effects on structures involves the knowledge of the parent population and extreme value distributions of the mean wind velocity. In spite of an impressive amount of measurements, refined probabilistic models and detailed applications to the study of specific sites, there is an equally disheartening lack of available probabilistic information at the territorial scale, and, therefore, of tools effectively applicable in the engineering and codification sectors. Almost all of the international standards and codes report sufficiently reliable maps of the mean wind velocity with 50-year return periods. On the other hand, there are still few regulations that provide the distribution of the yearly maximum value of the mean wind velocity or such value as a function of the return period. Furthermore, no regulations provide the distribution of the parent population of the mean wind velocity that may be very important for serviceability and fatigue analyses. This paper introduces a joint representation of the parent population and extreme value distributions of the mean wind velocity of synoptic extratropical cyclones; starting from this model, simple but reliable expressions are derived, directly applicable in the engineering and codification sectors, aimed at bridging the gap described. The obtained expressions are critically examined, pointing out their advantages but also some apparent critical issues. A preliminary application of these expressions is carried out with reference to the Italian territory. [ABSTRACT FROM AUTHOR]

Designing perforated steel beams is always a practical challenge in steel construction. There are a number of design methods available in the literature for design of these structural members. However, the range of applicability and accuracy of these methods in estimating the resistance of perforated beams is not known precisely. In this paper, an extensive statistical analysis is performed on numerical and laboratory test results to evaluate different formulas used to estimate the ultimate strength of perforated beams. Considered specimens include noncomposite steel beams with unreinforced openings of rectangular, circular, and elongated circular shape. The effect of different parameters including opening size, opening shape, moment to shear ratio, web slenderness ratio, and dimensional limits are discussed. Based on the results, all of the proposed relations are somehow conservative. However, one of the studied equations is found to give more reliable predictions for most of the cases. Finally, a trend analysis is performed to modify the equation presented in ASCE standard and results are verified against numerical and experimental data that showed a good agreement. [ABSTRACT FROM AUTHOR]

Design provisions for cold-formed steel (CFS) light frame shear walls with wall height-to-width/length ratios (aspect ratios) greater than 2:1, and less than 4:1, requires a reduction in nominal strength based on the wall aspect ratio. This reduction is attributed to increased wall flexibility. The current strength reduction is not supported by existing data and it is not justified given building code lateral displacement limits and the availability of expressions to estimate wall displacement. Additionally, a significant underestimation of nominal or peak strength is not helpful where capacity-based design is adopted. In this paper, the results of an experimental program that included 11-mm oriented strand board (OSB) sheathed CFS shear walls with aspect ratios between 2:3 and 8:1 are presented, and a conservative, more consistent and less severe strength reduction expression is offered-an expression that facilitates more sustainable design and meets the intention of the current standards of engineering practice. [ABSTRACT FROM AUTHOR]

Although the nonlinear behavior of rocking shallow foundations has been experimentally and numerically demonstrated as an effective tool to dissipate vibrational energy during seismic loading, the engineering community has yet to uniformly accept it as a targeted design mechanism for diffusing seismic energy in a structure. This paper presents results of a centrifuge test program that incorporated inelastic behavior into model building systems via yielding of both structural and foundation components. Three 2-story-1-bay building models were designed with similar layouts but different combinations of foundation and structural component yield strengths and were shaken with a similar suite of earthquake motions. Measurements of behavior of each of the model buildings are presented and cross-compared in terms of time history responses, hysteretic responses of the structural and foundation fuses, and maximum response parameters. A balanced design configuration, wherein the rocking foundation and structural fuse are intended to yield at approximately the same load, is demonstrated to be a well-controlled seismic-resisting system, with greatly reduced seismic ductility demand on the structural components. Moreover, seismic energy is well distributed among the targeted yielding components. In contrast, if the footing is restrained from rocking, the structural component ductility demand is significantly greater than that compared to its demand when the foundation is allowed to rock. In essence, the foundation rocking dominated model demonstrates its ability to protect the superstructure from seismic demands. In contrast, when the rocking foundation capacity is more than twice that of the structural fuse, rotations at the foundations are reduced significantly, at the price of much larger demands to the superstructure. [ABSTRACT FROM AUTHOR]

Wind-induced fatigue is a crucial topic in the design of wind-sensitive structures. Despite this, methods proposed in literature are mainly addressed to research, or they are too simplified for engineering applications. Thus, suitable engineering and standards procedures are almost totally lacking, which is a major shortcoming in structural and wind engineering. Starting from a closed-form solution (CFS) recently proposed by the authors, this paper develops a novel engineering approach to evaluate the alongwind-induced fatigue of structures and structural elements. This approach is based on a hierarchy of hypotheses that lead to a progressive simplification of the basic formulation. Two classes of formulas, referred to as Levels I and II CFSs, are obtained and critically discussed with special concern for input parameters. Level I CFS implies three further simplifications joined together by the common aim of providing refined approximations of the reference target solution. Level II CFS implies three different simplifications joined together by the common aim of providing easy solutions on the safe side. This set of CFSs is framed within a general procedure that any country, society, or engineer can easily personalize to a situation and requirement, ranging from numerical tools to manual engineering calculations and code provisions. [ABSTRACT FROM AUTHOR]

This paper presents a numerical finite-element parametric study on the behavior of transverse or longitudinal X-type plate-to-circular hollow section connections loaded under branch plate tension or compression, to evaluate the suitability of present international (CIDECT) design recommendations, the effect of boundary conditions and chord length, and the influence of applied chord normal stress. A total of 449 connections with wide-ranging values of geometric properties and chord normal stress levels were modeled and analyzed using commercially available software. An analysis of the effect of chord length determined that, to exclude the influence of chord end boundary conditions, an effective chord length of at least 10 times the chord diameter should be used for experimental and numerical studies. Further, the present CIDECT chord stress functions () provide an acceptable lower bound for all connections examined. Evaluation of present CIDECT partial design strength functions () indicated general conservatism, lack of plate thickness incorporation, and underutilization of tension-only connections. Partial design strength functions, determined through regression analysis, are hence proposed with lower-bound reduction (resistance) factors. [ABSTRACT FROM AUTHOR]

Earthquake engineering is increasingly using nonlinear response history analysis (RHA) to demonstrate the performance of structures. This rigorous method of analysis requires selection and scaling of ground motions appropriate to design hazard levels. This paper presents a modal-pushover-based scaling (MPS) procedure to scale ground motions for use in a nonlinear RHA of buildings. In the MPS method, the ground motions are scaled to match to a specified tolerance, a target value of the inelastic deformation of the first-mode inelastic single-degree-of-freedom (SDF) system whose properties are determined by the first-mode pushover analysis. Appropriate for first-mode dominated structures, this approach is extended for structures with significant contributions of higher modes by considering elastic deformation of second-mode SDF systems in selecting a subset of the scaled ground motions. Based on results presented for three actual buildings-4, 6, and 13-story-the accuracy and efficiency of the MPS procedure are established and its superiority over the ASCE/SEI 7-05 scaling procedure is demonstrated. [ABSTRACT FROM AUTHOR]

This paper reports on a study to extend a recently proposed direct displacement design (DDD) procedure for midrise engineered wood-frame structures and develop a set of factors for use in the procedure to meet specified performance levels with certain target probabilities. Representative index multistory building configurations were selected from the archetype buildings developed for the FEMA ATC-63. Seismic hazard levels and performance requirements recommended by ASCE 41-06 and modified for use in the National Science Foundation sponsored NEESWood project were used. The archetype buildings, originally designed using current force-based design procedures, were redesigned using the simplified DDD procedure (also described herein) with a range of nonexceedance (NE) probability adjustment factors (CNE). Specifically, the design interstory shear forces and the sheathing nail spacings were determined for each structure designed using CNE. Nonlinear time-history analysis was performed for each archetype structure under the 2%/50 year seismic hazard level and peak interstory drift distributions were developed. The NE probability at the 4% drift limit was then plotted against building height and design charts were developed for each different value of CNE. Given the building height and desired NE probability, engineers/designers can select the appropriate minimum value of CNE using these charts. Additional analyses could be performed to consider other hazard levels and performance requirements. Using design charts of this type, engineers/designers are able to specify a target drift limit as well as a target NE probability when using the simplified DDD procedure. Thus, a true performance-based procedure for the seismic design of midrise wood-frame structures is described. [ABSTRACT FROM AUTHOR]

This paper addresses the integrated design of civil engineering structures with control systems. Simultaneous optimization of such controlled structures is considered, showing that new alternative solutions can be achieved through integrated design. A procedure for design of controlled structural systems is developed using a two-stage approach: (1) a design of an optimal control system using a linear quadratic regulator algorithm; and (2) a redesign using an optimization procedure to match the performance of the controlled system obtained in (1). A linear single degree of freedom steel portal frame and a linear nine degree of freedom shear-type structure are used as examples to illustrate the feasibility of the proposed approach that reduces the structural weight of buildings by incorporating active or passive control elements while preserving the performance objectives. [ABSTRACT FROM AUTHOR]

The tensile capacity of concrete is usually neglected when calculating the strength of a reinforced concrete beam or slab, even though concrete continues to carry tensile stress between the cracks due to the transfer of forces from the tensile reinforcement to the concrete through bond. This contribution of the tensile concrete is known as tension stiffening and it affects the member’s stiffness after cracking and hence the deflection of the member and the width of the cracks under service loads. For lightly reinforced members, such as floor slabs, the flexural stiffness of a fully cracked section is many times smaller than that of an uncracked section, and tension stiffening contributes greatly to the postcracking stiffness. In this paper, the approaches to account for tension stiffening in the ACI, European, and British codes are evaluated critically and predictions are compared with experimental observations. Finally, recommendations are included for modeling tension stiffening in the design of reinforced concrete floor slabs for deflection control. [ABSTRACT FROM AUTHOR]

To reduce the floor-to-floor height, the technical, economical, and convenient (TEC) beam is developed as a new composite beam composed of structural tee, horizontal top stud, precast concrete, stirrup, and cast-in-place concrete slab. The preliminary testing of the proposed system was performed for simple beams, and the results indicated good structural behavior. However, application of the system in the relevant field requires the development of a moment-resisting connection using steel brackets on which upper rebars of the TEC beam are anchored. In this paper, three types of the proposed system are experimentally investigated under cyclic loadings. The parameters of the test are the spacing of transverse bars in the slab and the ratio of width of rebar spacing to bracket length. The structural behaviors such as load-displacement relation, ductility, variation of neutral axis, and failure pattern, were explored. Based on test results, specimens were classified as semirigid full strength by the Eurocode 4. It could be concluded that the proposed moment-resisting system shows good structural behavior and may be applicable in the field. [ABSTRACT FROM AUTHOR]

This paper proposes a new planar reinforced concrete (RC) formulation capable of modeling geometric and material nonlinearity. A new co-rotational sub-parametric formulation consisting of a four-noded element with quadratic hierarchic shape functions is presented. The novelty of this large-displacement-small strain element lies in the choice of the local coordinate system and the local degrees of freedom, which is mainly responsible for its simplicity and computational efficiency. For material nonlinearity, the Kotsovos and Pavlovic concrete model is used, with the addition of some numerical modifications including: (1) an accurate tangent stiffness for the nonlinear behavior of uncracked concrete; (2) a nonlinear uniaxial constitutive relationship for cracked concrete; and (3) exact cracking stress evaluation. Assuming perfect-bond, two layers of steel with only axial stiffness are smeared over the element according to their angles of orientation. Verification studies are presented to highlight the significance, limitations, and applicability of the proposed element in large displacement analysis of planar structures. [ABSTRACT FROM AUTHOR]

In this paper, a procedure is proposed for calculating the interaction diagram of a vertical pile group subject to axial load and biaxial moments; equations are then applied to the AASHTO LRFD code. Several cases are presented, depending on the efficiency of the pile group, and it is shown that the interaction diagram can be a pentahedron, a hexahedron, an octahedron, a nonahedron, or a decahedron. It is shown how the use of convex analysis and computational geometry leads to a rational calculation of the load effects and of the relationship between load effects and an interaction diagram. When the design entails evaluating several design alternatives, the methods of computational geometry yield a fivefold to tenfold computational saving with respect to considering all load combinations. A simple numerical example shows the application of the proposed procedure in a typical design setting, and highlights the advantages of the proposed procedure. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear model used to predict the load–deflection responses and axial load–moment interaction curves of pretensioned concrete-filled circular composite tubes. The model accounts for the prestressing effect, which not only improves serviceability, but also activates a confinement mechanism of the concrete core restrained by the tube. The enhanced performance of confined concrete is considered. In the compression side, the tube is modeled as a biaxially loaded membrane, subjected to longitudinal compressive and hoop tensile stresses, and failure is detected using the Tsai–Wu biaxial strength envelope. Progressive failure of layers of fibers at various directions within the tube leads to stiffness degradation, and is modeled using the classical lamination theory–ultimate laminate failure approach. The model is verified using experimental results and used in a parametric study to evaluate the effects of prestress level, amount and material type of prestressed reinforcement, and thickness and laminate structure of the tube. It was shown that ignoring concrete confinement would highly underestimate the flexural strength. The tube’s thickness and laminate structure have a much larger effect on flexural strength than the number of prestressing strands. [ABSTRACT FROM AUTHOR]

The focus of this paper is to describe the idea and the theory behind a finite-element model developed for analysis of timber trusses with punched metal plate fasteners (nail plates). The finite-element model includes the semirigid and nonlinear behavior of the joints (nonlinear nail and plate elements) and contact between timber beams, if any (bilinear contact elements). The timber beams have linear-elastic properties. The section forces needed for design of the joints are given directly by the finite-element model, since special elements are used to model the nail groups and the nail plate area over the joint lines. The finite-element model is based on the Foschi model, but with further improvements. After the theory of the model is described, results from experimental tests with two types of nail plate joints are compared with predictions given by the model. The model estimates the behavior of the joints very well at lower load levels. At higher load levels the stiffness is overestimated due to development of cracks in the timber and the linear-elastic timber properties in the finite-element model. [ABSTRACT FROM AUTHOR]

One challenge in the application of control systems to civil engineering structures is appropriate integration of a control system into a structure to achieve effective performance. Placement of control devices is strongly linked to the performance of a control system, and the most appropriate device placement scheme is strongly dependent on the performance objectives of the control system. Additionally, for the most effective control system, the placement scheme should be integrated with the design of the controller rather than sequential. This paper proposes an integrated technique to place devices and design controllers based on the use of genetic algorithms. The approach is flexible, allowing the designer to base the placement scheme on performance goals and/or system requirements. Active control devices are used and an H2/LQG controller based on acceleration feedback is selected for this study based on previous successes with this approach in civil engineering systems. To illustrate the proposed methodology, two numerical examples are considered. The first example considers a 40-story shear building, and the second is a full-scale, irregular, nine-story building. Control is achieved through the placement of one or more active control devices placed on various floors in an active bracing configuration. The improvements in the effectiveness of the proposed methodology as compared to previously developed techniques are demonstrated through comparative studies. [ABSTRACT FROM AUTHOR]

Recent terrorist attacks indicate the improvised explosive device as the choice terror tactic. Over the past decade, the U.S. Department of Defense has encouraged and sponsored research toward developing methods of reinforcing structures to protect building occupants from the effects of external explosion. The focus of wall reinforcement research has recently shifted from applying stiff fiber-reinforced composites to using lower-strength higher-elongation elastomeric polymers that can be easily applied to the wall interior. This paper presents recent efforts that have demonstrated an innovative use of thin-membrane elastomeric polymers to prevent breaching and collapse of unreinforced masonry walls subjected to blast. The complex array of failure mechanisms observed from recent explosive tests is discussed. Effects of structural and nonstructural parameters are described with the aid of finite-element simulations. Finally, the needs and direction of future blast reinforcement developments are outlined. [ABSTRACT FROM AUTHOR]

An exact formula is derived for the tangent geometric stiffness of inclined cables under self-weight. Comparisons are made with the well-known approximate formula by Ernst. It is found that the accuracy of Ernst’s formula deteriorates with increasing cable slackness and inclination. The error can be significant for certain configurations of the cable that are commonly used in such structures as cable-stayed bridges, guyed towers, electric transmission lines, and conductor cables connecting electrical substation equipment. An accurate and simple approximate formula is developed, which is applicable to a wide range of parameter values. [ABSTRACT FROM AUTHOR]

A multistory building with a large podium structure under earthquake excitation may suffer from whipping effect due to the sudden change of building lateral stiffness and mass at the top of the podium structure. An experimental investigation was carried out in this paper to explore the possibility of using magnetorheological (MR) dampers to connect the podium structure to the multistory building to prevent the whipping effect. The multistory building was constructed as a slender 12-story building model, whereas the podium structure was built as a relatively stiff three-story building model. A MR damper together with a current controller was used to link the three-story building to the 12-story building. The dynamic characteristics of the two buildings without any connection and with a rigid connection were first identified. The two building models without any connection and with the rigid connection were then tested under the scaled El Centro 1940 north–south ground motion. Finally, the two building models connected by the MR damper manipulated by a multilevel logic control algorithm were tested under the specified ground motion. The experimental results show that the MR damper with the multilevel logic control algorithm could significantly mitigate the seismic whipping effect and reduce the seismic responses of both the multistory building and podium structure. [ABSTRACT FROM AUTHOR]

Repetitive-member wall systems are among the most essential structural systems in conventional light-frame construction. Wood stud walls serve a variety of structural functions, particularly in regions of high natural-hazard risk, carrying axial forces, in-plane shear forces, and out-of-plane forces. This paper describes a structural analysis model for wood walls under transverse wind loads combined with either axial tension from wind uplift or axial compression from snow and live load suitable for reliability studies. The average model results compared well to available wall test data. Monte Carlo simulation was used in sensitivity studies of the transverse ramp-load behavior of walls under various levels of axial load. These simulations show that the model captures the range of possible behaviors of stud walls under various levels of axial load, both compression and tension. The model is accurate and simple enough to be used in reliability analyses, which will be described in a later paper. [ABSTRACT FROM AUTHOR]

The computational assessment of system reliability of structures has remained a challenge in the field of reliability engineering. Calculation of the failure probability for a system is generally difficult even if the potential failure modes are known or can be identified, because available analytical methods require determination of the sensitivity of performance functions, information on mutual correlations among potential failure modes, and determination of design points. In the present paper, a method based on moment approximations is proposed for structural system reliability assessment that is applicable to both series and nonseries systems. The point estimate method is applied to evaluate the first few moments of the system performance function of a structure from which the moment-based reliability index and failure probability can be evaluated without Monte Carlo simulations. The procedure does not require the computation of derivatives, nor determination of the design point and computation of mutual correlations among failure modes; thus, it should be computationally effective for structural assessment of system reliability. [ABSTRACT FROM AUTHOR]

The article discusses the acceptability of the basis for the ASCE 7 Standard peak-gust map as developed by wind engineers J.A. Peterka and S. Shahid (P&S). Peterka agree that the ASCE 7 map can be substantially improved. However, this goal cannot be achieved without a careful scrutiny and assessment of the methodology used to develop the map. The map need not be all on one page, as P&S suggest to justify their failure to account for significant wind climate differences between various regions. In fact, in the current version of the ASCE Standard the wind map is represented on five pages.

Similar to the definition of the moment-independent importance measure on model failure probability, the authors define the moment-independent importance measure concerning the importance sampling method. After combining the importance sampling procedure, the sampling efficiency is improved and the cost of computation is cheaper. After the moment-independent importance measures of all inputs are obtained, a new method called conditional importance sampling is proposed to calculate the failure probability and those inputs with high importance measures are chosen to be conditional variables. And state-dependent parameter method is employed in the new method. A numerical example and two structural engineering examples are used to demonstrate that the failure probability estimated by the proposed conditional importance sampling method is accurate and converges faster than those estimated by the traditional importance sampling method. [ABSTRACT FROM AUTHOR]

The article investigates the lateral stiffness of infilled frames, particularly focusing on the reduction of stiffness due to openings. The finite-element method is used to analyze various frame configurations. In the discussed paper, a new finite-element technique for the analysis of brickwork infilled plane frames under lateral loads has been presented. The basic characteristic of this analysis is that the infill/frame contact lengths and the contact stresses are estimated as an integral part of the solution, and are not assumed in an ad hoc way, as it is commonly used.