Journal of Structural Engineering

The strength of fillet weld groups, loaded with an out-of-plane eccentricity, is controlled by complex interactions of weld yielding, as well as bearing between the connected parts. Current models that characterize connection strength, including those used in North American design specifications, are highly conservative, leading to oversized welds. These models are phenomenological, because the internal stress distribution within the welds is difficult to characterize experimentally. A new model is proposed for characterizing the strength of these connections. The model is based on insights developed from sophisticated finite-element (FE) simulations that feature accurate measurements of weld profiles, multiaxial plasticity, and simulation of contact and gapping phenomena that strongly influence connection response. The FE simulations reveal that current models do not reflect key aspects of force transfer within the connection, especially on the compression side. The proposed model incorporates these insights by using stress profiles and mechanisms consistent with those implied by the FE simulations. The model is evaluated against 79 experiments from three test programs. It is determined that the new model greatly reduces the conservatism of the existing models, resulting in an average test-to-predicted ratio of 1.01. This is in contrast to previous models, for which the average test-to-predicted ratios are in the range of 1.33–1.77. The efficacy of the proposed model is analyzed with respect to various parameters, and its limitations are outlined.

In the steel design codes worldwide, the shear area for calculating the block shear capacity of a bolted connection is either the gross or the net shear area. The authors have previously noted independent experimental evidence indicating the shear failure planes to lie midway between the gross and the net shear planes, termed the active shear planes. This paper presents the nonlinear contact finite brick element analysis results that confirm the location of the active shear planes, indicated by regions of maximum shear stresses. The finite-element analysis also found that shear stresses approach zero toward the free downstream end of the connection block. The veracity of the active shear area is further demonstrated in terms of the ability of the resulting block shear equation to predict the governing failure modes of test specimens consistently, in comparison with the equations assuming the gross and the net shear areas.

This paper examines the accuracy of equations specified by the North American and Australasian steel structures codes for determining the net section tension capacity of a cold-formed steel angle brace bolted at one leg. The configurations tested in the laboratory include single equal angle, single unequal angle bolted at the wider leg, single unequal angle bolted at the narrow leg, double angles, and alternate angles. The steel materials used in the experiment are among those with the lowest ductility for which nominal tensile strength is permitted by cold-formed steel design codes to be fully utilized in structural design calculations. Based on a modification to the equation derived for channel braces bolted at the web, a design equation is proposed for determining the net section tension capacity of a cold-formed steel angle brace bolted at one leg. The proposed equation is demonstrated, through laboratory tests on 61 specimens composed of G450 sheet steel, to be more accurate than the code equations and those existing in the literature.

This paper investigated the accuracy of the AISC analysis methods in determining flexural strength of concrete-encased members. Analytical results from analyses performed using the AISC methods and a proposed method were compared with test data for 32 specimens. Results from this study showed that the method of superposition of elastic stresses and method of plastic stress distribution on the steel section alone overly underestimated flexural strength of the concrete encased composite members studied herein. On the other hand, the method of plastic stress distribution on the composite section, the method of strain compatibility, and the proposed method well predicted flexural strength of the encased composite members including members without shear anchors, suggesting that composite action can be developed in encased composite members without shear anchors when sufficient confinement is provided by transverse reinforcement. In addition, studies of effects of longitudinal and transverse reinforcement on flexural behavior of encased composite members were conducted to identify crucial parameters. The parameters examined herein included reinforcement ratio, steel flange area, steel shape depth, and transverse reinforcement spacing. Implications and recommendations drawn from the studies are discussed.

Steel jacketing has been widely used for strengthening RC columns in the last four decades. In practice, the RC columns to be strengthened are usually subjected to eccentric precompressed axial loads. Until now, there have been only limited studies conducted that address the stress-lagging effects between the original column and the new jacket due to the preexisting load. In this paper, the precambered steel plate–strengthening approach, which can alleviate the stress-lagging effects, was adopted to improve the axial strength and moment capacity of the preloaded RC columns subjected to eccentric compression loading. An experimental study that involved eight specimens with different eccentricities, plate thicknesses, and initial precamber displacements was conducted to examine the ductility and moment-curvature response of strengthened columns and to validate the effectiveness of this approach. A theoretical model was developed to predict the axial load capacity of the plate-strengthened columns. A comparison of the theoretical and experimental results showed that the theoretical model accurately predicted the axial load-carrying capacities of the plate-strengthened columns under eccentric compression loading.

In this study, the cyclic seismic performance of a concrete-filled U-shaped steel beam to H-shaped steel column connections was experimentally evaluated. The concrete-filled U-shaped steel beams were compositely attached to the concrete floor slab. The test was conducted in two stages. The first testing program was carried out on one-sided moment connections to find the most promising connecting scheme. The strengthening scheme, or welding steel plates to the beam bottom flange with minimized stress concentration, was shown to be the most satisfactory, and it was used in the second-stage test on two full-scale cruciform specimens. Considering the unique constructional nature of the proposed composite connections, the critical limit states such as weld fracture, local buckling, concrete crushing, and rebar buckling were carefully addressed in designing specimens. Test results showed that the connection details and design procedures proposed in this study can successfully control the critical limit states mentioned previously. The proposed connection detail successfully pushed the plastic hinging to the tip of the strengthened zone as intended in design, thus effectively protecting the more vulnerable beam-to-column welded joint. The specimens typically exhibited a maximum story drift capacity of more than 5.5% rad, exceeding the minimum limit of 4% rad required of special moment frames. Four of the five specimens tested in this study eventually failed because of a low-cycle fatigue fracture across the beam bottom flange at a high story drift greater than 5.0% rad.

Previous research on steel plate shear walls (SPSWs) and current design codes have focused principally on achieving highly ductile behavior through stringent detailing requirements. As such, the system is generally considered to be economical only in high-seismic regions. However, lower demands in other regions may permit the use of more economical options. This paper describes a proposed concept for SPSWs that meets the intent of capacity design, while greatly improving competitiveness in seismic regions where maximum ductility is not required. A large-scale, 2-story SPSW specimen was tested to evaluate the associated performance. The wall had standard double-angle beam-to-column shear connections and was tested under vertical gravity load concurrent with reversing lateral loads at each floor level. The specimen survived 25 lateral load cycles, 18 of which were in the inelastic range. The test results indicated that excellent performance can be expected in low-seismic regions, despite significantly reduced costs, compared with traditional designs. The shear wall showed stable performance at large lateral deformation ratios with high levels of ductility and energy dissipation capacity.

The objective of the research presented in this paper is to investigate, experimentally, the effect of material- and section-level parameters on the structural response of concrete and engineered cementitious composite (ECC) buildings. In addition to testing of columns under monotonic, cyclic, and static-time history loading, hybrid simulation of structural frames is conducted. Stiffness, strength, ductility, and energy absorption capacity are selected as the response measures that represent the behavior of structures under seismic actions. The investigated variables are reinforcement ratios, ECC material properties, and axial load levels. The results are proposed as basic guidelines to determine the performance enhancement in terms of stiffness, strength, ductility, and energy absorption capacity, which could be achieved by replacing concrete with the high-performance material ECC.

Unreinforced masonry (URM) structures represent a significant portion of the residential building stock of the central and eastern United States. Fifteen percent of homes in the eight-state region impacted by the New Madrid Seismic Zone are URM buildings. The brittle nature of URM buildings further supports a thorough consideration of seismic response given the susceptibility to severe failure modes. Currently, there is a pressing need for analytically based fragility curves for URM buildings. To improve the estimation of damage-state probabilities through the development of simulation-based URM fragilities, an extensive literature survey is conducted on pushover analysis. Using these data, capacity curves are generated, from which damage performance limit states are defined. Demand is simulated using synthetically derived accelerograms representative of the central and eastern United States. Structural response is evaluated using an advanced capacity spectrum method. Capacity, demand, and response are thus derived analytically and utilized to generate a more reliable and uniform set of fragility curves for use in loss-assessment software. This paper presents a framework amenable to rapid, flexible updating that, with the appropriate database of studies, is capable of producing curves representative of any URM building typology subjected to a specified hazard. The curves are expressed in multiple forms to demonstrate capability of use in various loss-assessment applications.

Hybrid masonry is an innovative technology for seismic design of buildings. The system uses reinforced masonry panels within a steel-framed structure, where steel connector plates link the steel frame to the masonry panels. The system has been used for construction of low-rise buildings in the low-seismic regions of the eastern and midwestern United States but has not been implemented in regions of moderate or high seismicity yet. Current research is underway to extend the application of hybrid masonry for use in high-seismic regions. In this paper, the overall approach for seismic design of one type of hybrid masonry systems is studied, and the steps of a capacity design process are presented, where two favorable ductile modes of behavior may be exploited: steel connector plates behaving as fuses or flexural yielding of the masonry panels. Moreover, this research applies the two design options for 3-, 6-, and 9-story prototype buildings located in a high seismic region and evaluates viability of hybrid masonry as a new seismic lateral-load resisting system. On the basis of this design framework and the exploratory studies, both approaches are shown to be feasible for developing realistic system configurations. Nevertheless, for the case of flexural yielding of the masonry panels, the steel connector plates must carry significant shear force demands. The structural system then requires more hybrid panels compared with corresponding systems when plasticity is concentrated in the steel connector plates.

Structures deteriorate as a result of material aging, aggressive environmental conditions, and increasing loads. During their lifetime, structures are also possibly exposed to some extreme events. The associated consequences of failure caused by progressive deterioration or extreme events can be devastating. Therefore, risk assessment and risk mitigation are necessary to keep structural performance within tolerable levels. This paper proposes an approach for assessing the time-dependent risks caused by traffic and earthquake loads and establishing the optimal preventive and essential maintenance strategies of bridges. The efficiency of the proposed approach is demonstrated using a highway bridge. Socioeconomic and environmental losses are investigated in a consequence-based framework. The vulnerability analysis under traffic loads is performed using time-dependent deterioration and traffic load models. The time-dependent failure probability for given earthquake loads is computed by comparing displacement ductility capacity and demand obtained via nonlinear dynamic analysis. The risks from 196 earthquake scenarios associated with four magnitudes and 49 earthquake strike locations are compared, and the highest one is selected as representative of the seismic risk. Based on the available maintenance options and the associated costs, the optimal lifetime essential/preventive maintenance strategies for total risk mitigation are developed.

This paper proposes a generalized probabilistic framework for optimum inspection and maintenance planning of deteriorating structures. The proposed framework covers (1) the damage occurrence and propagation and service life prediction under uncertainty, (2) the relation between degree of damage and probability of damage detection of an inspection method, and (3) the effects of inspection and maintenance on service life and life-cycle cost. Optimum inspection and maintenance types and times are obtained through an optimization formulation by maximizing the expected service life and minimizing the expected total life-cycle cost consisting of inspection and maintenance costs. The service life, life-cycle cost, and maintenance delay, along with inspection and maintenance actions, are formulated using a decision tree model. The selection of the appropriate maintenance type depends on the degree of damage. The proposed framework is general and can be applied to any types of deteriorating structures or materials. Applications of the proposed framework may include, but are not limited to, bridges, buildings, aircrafts, and naval ships.

Straw bale construction is a nonconventional technique that involves stacking common straw bales and then applying layers of plaster to form load-bearing walls. The straw bales provide insulation, whereas the plaster protects the bales from moisture and provides strength and stiffness for the wall. This technique has experienced a revival because of its environmental benefits. Because there are few codes and standards for this construction technique, engineers are often required to check and approve designs using straw bale construction before building permits will be issued. An understanding of the behavior of straw bale construction is needed for engineers to approach this system with confidence. A model for predicting the response of plastered straw bale walls subjected to concentric and eccentric compressive loading was proposed in this paper. The model was verified using experimental tests of wall panels loaded until failure. The eccentrically loaded specimens were found to have load-deflection behavior (lateral and vertical) that could be predicted by theoretical models based on the stress-strain behavior of the lime-cement plaster. Failure of the specimens was observed to occur as a result of compressive failure of the plaster and was predicted based on the theoretical models.

One of the problems encountered in the estimation of wind effects on high-rise structures is the development of combinations of wind-induced translational responses in possible conjunction with rotational responses and/or of forces and moments that contribute to the wind-induced demand at various cross sections of individual structural members. In current wind engineering practice such combinations are developed in large part intuitively because phase information on the effects being combined is not readily available from frequency domain analyses. In contrast, full time series analyses can produce estimates of combined wind effects because they preserve phase information; however, such analyses can be overly time-consuming. In current wind engineering practice it is common to use the empirical point-in-time (PIT) procedure for the estimation of peaks of combined stationary stochastic processes. The procedure is applied to pairs of such processes, and consists of adding an estimate of the peak value of one of the processes to the estimated value of the second process at the time of the occurrence of that peak. Even if the full time histories of the two stochastic processes are used, errors inherent in PIT can be in some cases as high as 20% on the unconservative side. The purpose of this paper is to present the empirical multiple points-in-time (MPIT) procedure, which improves significantly upon the PIT approach. The MPIT procedure is illustrated by an application to a 60-story reinforced concrete structure. Results show that the MPIT approach produces remarkably accurate estimates of the peak combined wind effects by using a limited number of peaks from the time histories of the individual wind effects being combined. Those estimates are obtained far more economically in terms of computational time than conventional time domain estimates that use full time histories.

In the case of nonproportionally damped structures, the forced decoupling method is often adopted in approximate analysis. However, it generally cannot satisfy the precision requirements for practical engineering. Taking this into account, methods to calculate the stochastic seismic response of nonproportionally damped structures are systematically studied in this paper. Based on the pseudoexcitation method, an efficient and accurate iteration method with the advantages of high computational efficiency and iteration convergence is also proposed. This new method is preferred for practical engineering because of real expressions. Finally, a numerical example is carried out to verify the properties and advantages of the proposed method.