Journal of Structural Engineering

Performance-based earthquake engineering aims to quantify performance of facilities using metrics that are of immediate use to both engineers and stakeholders. A rigorous yet practical implementation of a performance-based earthquake engineering methodology is developed and demonstrated for an idealized building. The methodology considers seismic hazard, structural response, resulting damage, and repair costs associated with restoring the building to its original condition, using a fully consistent, probabilistic analysis of the associated parts of the problem. The methodology can be generalized to consider other performance measures such as casualties and down time, though these have not been pursued. The proposed procedure is consistent with common building design, construction, and analysis practices such that it can be readily adopted in earthquake engineering practice today.

This paper provides an approach to conduct a probabilistic assessment of structural damage due to seismic events with an application to typical building structures in mid-America. The developed methodology includes modified damage state classifications based on the Applied Technology Council (ATC)-13 and ATC-38 damage states and the ATC-38 database of building damage. Damage factors are assigned to each damage state to quantify structural damage as a percentage of structural replacement cost. To account for the inherent uncertainties, these factors are expressed as random variables with a Beta distribution. A set of fragility curves, quantifying the structural vulnerability of a building, is mapped onto the developed methodology to determine the expected structural damage. The total structural damage factor for a given seismic intensity is then calculated using a probabilistic approach. Prediction and confidence bands are also constructed to account for the prevailing uncertainties. The expected seismic structural damage is assessed for three types of building structures in the mid-American region using the developed methodology. In addition, a sensitivity analysis for the probabilistic parameters is conducted. The developed methodology provides a transparent procedure where the structural damage factors can be updated as additional seismic damage data becomes available.

This paper presents several results of a wide experimental program undertaken to evaluate the seismic performance of RC columns, externally confined with fiber-reinforced polymers (FRPs). Specimens consisted of full scale square columns, 300 mm on each side, reinforced by using both smooth and deformed steel rebars and subjected to a constant axial load and monotonic or cyclic flexure; in particular, two levels of the axial load were considered. Tests were conducted, in displacement control, on both FRP confined and unconfined RC columns: the confinement system was obtained by partially wrapping two or four unidirectional carbon (CFRP) or glass (GFRP) fiber layers around the member; additionally, some tests were performed on members strengthened by using both the external CFRP wrapping and longitudinal steel angles. Experimental results allowed evaluating depending on the level of applied axial load and on the type of steel rebars adopted for reinforcing each column—the benefits introduced by the considered strengthening systems in terms of strength, ductility, and energy dissipation capacity.

Three nonseismically detailed interior reinforced concrete beam-column joints, namely, one eccentric and two concentric joints, strengthened with proposed fiber-reinforced polymer (FRP) wrapping configurations using glass fiber-reinforced polymer and carbon fiber-reinforced polymer strips and sheets, were tested under constant axial compression load and reversed cyclic loading which simulated low to moderate earthquake forces. Seismic performance of the strengthened beam-column joints in terms of their hysteresis response, stiffness, and energy dissipation capacity is evaluated and compared to those of the original and unstrengthened beam-column joints. Results indicate that applying strips at 45º on a flushed eccentric joint core and as cross bracing on the beam and confinement round the column is very effective. All specimens failed with gradual strength deterioration, bond degradation, and debonding of FRP sheets was observed near the joint core. The proposed strengthening schemes were found to be efficient and economical for mass repair or upgrading of nonseismically detailed structures.

This paper introduces a novel type of heat transfer finite element that can be used to model the three-dimensional thermal response of structural beams and columns subjected to elevated temperatures associated with fire. The element is a three-node heat transfer element that uses a fiber discretization to account for both transverse and longitudinal temperature variations in a structural member. This fiber heat transfer element is purposely formulated to be compatible with any fiber beam-column finite element in a sequentially coupled thermal-mechanical analysis of a structural frame subjected to fire. The element is implemented in ABAQUS using a user-defined element subroutine. To demonstrate the capabilities of the fiber heat transfer element, analyses are performed on members with various types of thermal boundary conditions. Results indicate that the fiber heat transfer element offers excellent accuracy with minimal computational expense, making the fiber heat transfer element a valuable tool for modeling the behavior of frame structures in fire.

In this paper a robust nonlinear finite-element procedure is developed for three-dimensional modeling of reinforced concrete beam-column structures in fire conditions. Because of the changes in material properties and the large deflections experienced in fire, both geometric and material nonlinearities are taken into account in this formulation. The cross section of the beam column is divided into a matrix of segments and each segment may have different material, temperature, and mechanical properties. The more complicated aspects of structural behavior in fire conditions, such as thermal expansion, transient state strains in the concrete, cracking or crushing of concrete, yielding of steel, and change in material properties with temperature are modeled. A void segment is developed to effectively model the effect of concrete spalling on the fire resistance of concrete beam-column members. The model developed can be used to quantify the residual strength of spalled reinforced concrete beam-column structures in fire. A series of comprehensive validations have been conducted to validate the model. From this research, it can be concluded that the influence of transient state strains of concrete on the deflection of structures can be very significant. However, there is very little effect on the failure time of a simple structural member. The impact of concrete spalling on both the thermal and structural behaviors of reinforced concrete members is very significant. It is vitally important to consider the prospect of concrete spalling in fire safety design for reinforced concrete buildings.

This paper presents the formulation for a novel flexibility-based one-dimensional (1D) finite element that captures material and structural softening within a reinforced concrete framed structure. Separating the total elastic and inelastic components of the strain at integration points, a secant solution strategy is introduced that is consistent with damage models in the framework of nested iterative algorithms. In this formulation and solution strategy, at every stage of loading the inelastic deformation of the element can be obtained directly without resorting to unloading processes, which is useful when the value of inelastic deformation is required according to some seismic design provisions. In addition, a nonlocal integral damage model, based on averaged strain, has been used to ensure mesh size independent objectivity of local and global responses. The efficiency and accuracy of the formulation is compared with numerical and experimental data with good correlation observed and mesh objectivity demonstrated.

Steel plate shear walls (SPSWs) have become an increasingly popular lateral force resisting system in buildings. Although originally conceived to resist earthquake forces, recent developments raised questions as to the ability of SPSWs to resist blast loading, whereby the plate would resist out-of-plane impulsive pressures. To investigate this, two 0.4-scale single story SPSW specimens, representing the first story of a four story prototype SPSW, were fabricated and subjected to explosive charges. The out-of-plane resistance of the infill plate was analyzed using nonlinear finite-element analysis (FEA) and yield line theory. Results of these analyses showed the out-of-plane resistance is governed by the large deformations and inelastic material behavior and that yield line theory significantly underestimated the out-of-plane resistance in comparison with the finite-element analysis for infill plates typical of SPSW construction. Based on these results a simplified plastic analysis procedure is proposed to estimate the out-of-plane resistance of SPSW infill plates that is shown to agree well with the results of the FEA. Results of the experimental investigation showed the SPSW had a limited capacity to resist out-of-plane blast loading and that the typical seismic detail for connecting the infill plate to the boundary frame might not be appropriate for blast applications.

A series of shallowly embedded steel column base consisting of an exposed column base and a covering reinforced concrete floor slab were tested under horizontal cyclic loading to very large deformation. By adjustments to the floor slab thickness, shape, and reinforcing bars in the slab, the initial stiffness, maximum strength, and dissipated energy of the shallowly embedded column base increase significantly with respect to those of the exposed column base. It is found to be practical to strengthen the shallowly embedded column base so that it would behave like a fully embedded column base. Punching shear failure in the floor slab around the column due to the uplift of the base plate occurs when the shallowly embedded column base fails. Based on the plastic theory, a mechanical model that considers the contributions of the anchor bolts and the bearing and punching shear of the floor slab is proposed to evaluate the maximum strength. The evaluated results have good agreement with the test results, with errors not greater than 20%.

Double skin composite walls are composed of two steel plate “skins” connected by tie bars, with the space between them filled with concrete. They were developed to reduce wall thickness, to enhance constructability, and to enable rapid construction by eliminating the use of formwork and reinforcing bars. In the present study, cyclic testing was performed to investigate the seismic behavior of isolated and coupled double skin composite walls with rectangular and T-shaped cross sections. The wall specimens failed mainly by tensile fracture of the welded joints at the wall base and coupling beams, or by local buckling of the steel plates. Because of their large depth, the ductility of the wall specimens was not as good as that of beams having less depth. In particular, the ductility of the walls was significantly affected by the strengthening methods used for the wall base. The load-carrying capacities of the isolated and coupled wall specimens were evaluated using plastic stress distributions in their cross sections, which provided satisfactory predictions.

Concrete-filled tubes (CFTs) are columns commonly used in high-rise building construction due to their structural effectiveness. Past studies on CFT have focused primarily on uniaxial compression, bending, and eccentric compression and a few investigations have studied member behavior under combined compression and torsion. In this paper, the behavior of a circular CFT column under combined torsion and compression was theoretically investigated considering the confinement effect of the steel tube, softening of concrete, and spiral effects. Biaxial stress effects due to diagonal cracking were also considered. By incorporating these factors into the compatibility and equilibrium conditions, a basic equation to describe the torsional behavior of the entire loading history of CFT members was derived.

A computer-based strut-and-tie model formulation procedure is presented, allowing the nonlinear cyclic response of an entire reinforced concrete structural system to be investigated. Load-carrying capacity and the failure sequence of structural components resulting from localized damage are predicted. In addition, a hybrid modeling solution strategy that incorporates nonlinear strut-and-tie models into the conventional planar frame modeling technique is proposed. This hybrid solution minimizes the computational time required to perform nonlinear analysis of large concrete frame structures in which accurate modeling of the disturbed regions is critical. Advantages and deficiencies of the proposed nonlinear analyses with respect to conventional methods are also demonstrated.

Stone masonry is the oldest building material that survived until today, being used all over the world, particularly in impressive historic structures as an evidence of the achievements of ancient cultures. Stone walls are usually understood as structural elements able to withstand compression but they can also act as elements that provide resistance against in-plane wind and earthquake actions. Still, only a few experimental investigations are available in the literature, regarding the in-plane behavior of stone masonry walls under cyclic loading. The present work aims at obtaining a better insight on the behavior of stone masonry walls under cyclic in-plane loads. For this purpose, 23 walls were tested under different vertical normal stress level and different bond arrangement that represent typical walls typologies. The experimental results indicate these two factors play an important role on the in-plane behavior of stone masonry walls. In particular, ductility and energy dissipation depend significantly on the textural arrangement of the stones. It is also demonstrated that good quality stone masonry walls exhibit large nonlinear deformation capacity, with moderate damage levels. Finally, it is shown that the lateral resistance of stone walls provided by simplified analytical methods agrees reasonably well with the experimental results.

In current design codes, structural fire behavior is evaluated by conducting experiments on isolated structural elements in a standard fire condition. In such tests involving single isolated elements, many aspects of structural behavior that occur due to the interaction between adjacent members as well as the role of connections cannot be studied. Performance of real structures subject to fires is often much better than that predicted from standard tests due to structural continuity and the interaction between members. In addition, tests performed under the current design codes subject the structural element to a heat up phase only and do not consider the cool-down phase during which local/global failure of the structure may occur. This paper describes the results of a furnace test conducted on two full-scale composite steel frames. In one frame the beam-to-column connections were protected while in the second frame the columns as well as the beam-to-column connections were protected. A special test furnace was built in which full-scale frames could be tested under load. The structural frame was subjected to a heat up phase followed by a cool-down phase. During the test, the furnace temperature, steel and concrete temperatures as well as the horizontal and vertical deflections were recorded. The complete deformation process of the test frame observed during the heating phase and the cooling phase, including failure of the frame is described in this paper. A comparison of the data obtained from the two tests indicates that the fire resistance of a composite beam is significantly better than that of a steel column. Finally, experimental data on fire resistance of composite frames with conventional floor slab construction was compared with data from slim floor slab construction. Results indicate that the fire resistance rating of frames constructed with slim floor slabs is at least as good as that of frames with conventional floor slab construction. It is proposed that in certain engineering design scenarios, the composite beam may not have to be protected due to its higher fire resistance rating, while the steel column should be protected from fire heating.

The parametric approach to eliminating the temperature-caused modal variability in vibration-based structural damage detection requires a correlation model between the modal properties and environmental temperatures. This paper examines the generalization capability of neural network models, established using long-term monitoring data, for correlation between the modal frequencies and environmental temperatures. A total of 770 h modal frequency and temperature data obtained from an instrumented bridge are available for this study, which are further divided into three sets: training data, validation data, and testing data. A two-layer back-propagation neural network (BPNN) is first trained using the training data by the conventional training algorithm, in which the number of hidden nodes is optimally determined using the validation data. Then two new BPNNs are configured with the same data by applying the early stopping technique and the Bayesian regularization technique, respectively. The reproduction and prediction capabilities of the two new BPNNs are examined in respect of the training data and the unseen testing data, and compared with the performance of the baseline BPNN model. This study indicates that both the early stopping and Bayesian regularization techniques can significantly ameliorate the generalization capability of BPNN-based correlation models, and the BPNN model formulated using the early stopping technique outperforms that using the Bayesian regularization technique in both reproduction and prediction capabilities.

This technical note describes how full-scale observations of external pressure coefficients for a single storey industrial building located in Quebec City, Canada compared with matched scale at 1:200 wind tunnel measurements. Wind pressure was measured by a grid of 20 pressure taps at wall and roof surfaces. Both mean and peak pressure coefficients on the envelope of the actual building compare well with values obtained in the wind tunnel.