Journal of Structural Engineering

Ground motions recorded during earthquakes are often used to assess the seismic performance of structures affected by those ground motions. However, it is necessary to first establish the return period of the recorded ground motion, because structures are expected to perform better for frequently occurring ground motions than for rare ground motions. A systematic approach is presented to establish the return period of ground motion recorded at the base of the Templeton Community Hospital during the 2003 San Simeon California Earthquake. A similar approach can be used for any other ground motion.

The recently developed drift spectrum is extended to buildings that do not deform laterally like pure shear beams. Similarly to Iwan’s drift spectrum, the proposed generalized interstory drift spectrum uses a continuous linear-elastic model to obtain estimates of interstory drift demands in buildings. However, the generalized interstory drift spectrum is based on a continuous model that consists of a combination of a flexural beam and a shear beam, rather than only a shear beam. By modifying one parameter the model used in the proposed generalized interstory drift spectrum can consider lateral deformations varying from those of a flexural beam to those of a shear beam. Hence, it permits us to account for a wide range of modes of deformation that represent more closely those of multistory buildings. The proposed generalized interstory drift spectrum is based on modal analysis techniques that are familiar to structural engineers and uses a damping model that avoids the problems that can occur in the drift spectrum. The generalized interstory drift spectrum is illustrated with various recorded ground motions. The effects of damping, higher modes, and lateral stiffness ratio are investigated and discussed.

Coupled building control has been shown to be an effective means of protection for flexible building structures. Numerous researchers have proposed various active, passive, and semiactive coupled building control strategies for both high-rise and low-rise buildings. Actual applications of coupled building control for low-rise buildings and high-rise buildings have been successfully implemented in Japan using passive and active control technology. Much of the research in the literature has focused on specific building pairs. To date, there have been no detailed studies of the effects of the building configuration and connector location on the overall system performance. This paper examines these effects and compares the efficacy of passive and active coupled building control for flexible adjacent buildings.

This paper presents an innovative structural system, named weld-free system, developed to overcome the difficulty in the quality assurance encountered in construction of steel moment resisting frames with conventional welded connections. The proposed structural system adopts a mechanical joint equipped with metallic-yielding damper as beam-to-column connection, wherein slip-critical joints are made by recently developed super high-strength bolts. The structural configuration and load-carrying mechanism of weld-free steel structures are described herein. Key features of the super high-strength bolts are also introduced. Furthermore, an experimental verification is presented. Cyclic tests were conducted on full-scale models of weld-free beam–column subassemblies and one base-line specimen with conventional welded connection. The test results clearly reveal the efficiency of the weld-free system in enhancing large and stable hysteresis loops while maintaining the beams and columns virtually in the elastic range until the ultimate state of the structure. It is also verified that the load-carrying mechanism of weld-free systems can be predicted very well by the presented theoretical solutions.

The procedure of direct displacement-based design (DBD), presented in the SEOAC Blue Book, was modified to evaluate the seismic performance of existing structures. Then an optimum number of velocity-dependent supplemental dampers, such as viscous and viscoelastic dampers, required to reduce the seismic response of existing structures to a given performance limit state was evaluated. The proposed method was applied to seismic performance evaluation and performance-based seismic retrofit of ten- and 20-story steel frames, and the final design was verified by time history analyses using artificial earthquake records generated based on the design spectrum. According to the analysis results, the performance points evaluated by the proposed method match well with those computed by time-history analyses, and the maximum displacements of the model structures retrofitted by the supplemental dampers corresponded well to the given target values.

This paper presents analytically developed seismic fragility curves for unattached bench-mounted equipment considering representative building, bench, and equipment interface properties. The emphasis of the study is on rigid scientific equipment, which is often placed on the surface of ceramic laboratory benches in science laboratories or other buildings. The paper first addresses the inherent uncertainty in the frictional behavior of the equipment supported on benches (defined by the static and kinetic coefficients of friction, ${\mu }_s$ and ${\mu }_k$ , respectively) and then describes the resulting variability of their sliding response when subjected to earthquake motions. Seismic fragility curves are generated for these types of equipment, considering 32 short distance ground motions of different hazard levels, propagated through three different building models. It is observed that although the variation in response is highly sensitive to the uncertainty in ${\mu }_s$ and ${\mu }_k$ , this variability does not propagate to the fragility curves. Moreover, accounting for the supporting bench and building characteristics are shown to significantly affect the shape and distribution of the fragility curves. From these results, considerations for design are proposed.

Alongwind actions on structures may produce a great number of stress cycles and lead to significant damage accumulation. A critical analysis of the pertinent methods proposed in the literature provides evidence of the necessity of improving the level of approximation, taking into account the bandwidth spectral properties of the stress processes. This paper pursues this aim by establishing an advanced broadband formulation. Applying the cycle counting method based on the narrow-band assumption, two discrete cycles histogram expressions are first suggested, which lead to an upper and lower bound of the fatigue damage. As the gap between the two bounds may be very large, a more refined counting method is formulated, based on a bimodal representation of the alongwind induced stress power spectral density functions; the low- and high-frequency spectral contents are associated, respectively, with the quasistatic and the resonant parts of the response. Some examples highlight the properties of the proposed procedure and show the good agreement between the bimodal approach and the numerical results.

Database-assisted design (DAD) is becoming a realistic possibility whereby archived wind pressure time series on building envelopes from wind tunnel experiments are directly used in structural analysis software for building design. In order for DAD to be of practical use, a data handling system is required. The main task of the system is to perform interpolation in order to obtain wind pressure time series beyond the basic configurations available in the database. The functional dependence of the pressure coefficients is reduced to geometric variables only, greatly simplifying the process of interpolation. It is shown that all interpolation schemes require estimation of the first and second order statistical moments.

This paper describes a finite element model for the characterization of the nonlinear behavior of bolted T-stub connections that idealize the tension zone of bolted joints. Two different types of T-stub elements are considered: rolled profiles that are cut along the web, and two plates, flange and web, that are welded in a T shape by means of a continuous fillet weld. The results of existing experimental work are used to calibrate the models. It is found that the numerical approach allows the quantitative actual response to be accurately reproduced. In the case of welded T-stubs, the differences between the numerical model and the experiments are greater due to the effects of residual stresses and modified mechanical properties close to the weld toe, which are not easy to quantify. A parametric study is also undertaken to provide insight into the overall behavior, failure modes, and deformation capacity of the various specimens. A proposal for prediction of failure criteria of these simple connections is also presented and discussed.

A strut-and-tie design methodology is presented for three-dimensional reinforced concrete structures. The unknown strut-and-tie model is realized through the machinery of a refined evolutionary structural optimization method. Stiffness of struts and ties is computed from an evolved topology of a finite element model to solve statically indeterminate strut-and-tie problems. In addition, compressive strength for struts and nodal zones is evaluated using Ottosen’s four-parameter strength criterion. Numerical examples are studied to demonstrate that the proposed design methodology is suitable for developing and analyzing three-dimensional strut-and-tie models for reinforced concrete structures.

Fatigue of reinforced concrete (RC) bridge slabs is analyzed based on crack bridging degradation concept. RC slabs are typically subjected to a large number of load repetitions due to traffic, and their failure processes are characterized by progressive concrete cracking. This study applies the recently developed fatigue analysis method based on crack bridging degradation to slab problems. The bridging stress degradation of concrete cracks is introduced as a primary mechanism for the propagations of cracks that induce failure. A three-dimensional finite element method, which consists of smeared crack elements for concrete and rod element as reinforcing bars, is proposed. The fatigue life and its failure patterns are focused on. The analysis of RC slabs under different loading conditions demonstrates that the slab under moving load exhibits shorter fatigue life and more severe damage than that under fixed pulsating load. The extension of fatigue life due to underlay and overlay repairs is evaluated numerically. All repaired slabs exhibit a large extension of fatigue life and a reduction of midspan deflection when compared with the original slab.

This paper presents an analytical procedure for predicting the shear load-deformation response of concrete filled fiber-reinforced polymer (FRP) composite cylindrical shells with full- and noncomposite behavior. The approach is based on a sectional layered analysis with an iterative algorithm to achieve equilibrium and compatibility conditions of the FRP/concrete system, including the cracked behavior of the FRP-confined concrete, until first-ply failure of the FRP composite. The model follows first order mechanics for the shear behavior of structural members in combination with a smeared shear modulus for cracked concrete and inclusion of extension/shear coupling effects of anisotropic FRP laminates. Comparisons of the analytical response with available experimental data from large- and small-scale tests were found to be in reasonable agreement and corroborated the significant influence of the concrete core and the composite interaction details on the shear load-deformation response. Parametric studies on the influence of concrete properties, axial loads, and FRP laminate design are discussed.

An assessment of the structural performance of concrete tunnel linings under fire load is presented for the Lainzer Tunnel, a shallow tunnel recently constructed in Austria. Prior to the installation of the concrete lining at this tunnel, large-scale temperature experiments were conducted, revealing almost no reduction of the lining thickness in consequence of spalling for the employed lining concrete, reinforced by polypropylene fibers. In the absence of spalling, dehydration of concrete under high temperatures is the safety-determining process. Within the thermochemomechanical material model employed for the tunnel-safety assessment presented in this paper, dehydration is described by the decrease of the hydration extent, resulting in the reduction of both stiffness (thermal damage) and strength (thermal decohesion). The distribution of the hydration extent is determined by means of a thermochemical analysis. The obtained results serve as input for the subsequent chemomechanical analysis, providing insight into the deformation state of the ground-lining compound structure and the stress state in the lining. As a function of the stress state, a level of loading $\mathcal{L}$ is introduced, with $\mathcal{L}=0$ for the unloaded material and $\mathcal{L}=100\%$ for stress states reaching the compressive strength of concrete. During fire exposure the size of $\mathcal{L}$ increases because of increased loading by thermal expansion, on the other hand, and because of thermal decohesion resulting in a reduction of the compressive strength, on the other hand. The difference between 100% and $\mathcal{L}$ represents the remaining load-carrying capacity of the lining, giving access to the safety of the tunnel for the chosen fire-accident scenario.

The “form finding” methods for tension structures may be classified into two different groups: the linear and nonlinear methods. One of the linear methods is the force density method (FDM). In this paper advantage is taken of an important property of the FDM by which knowledge of the initial position of the nonfixed nodes of the structure is not needed, only the connectivity of the nodes is necessary for the solution of the problem. Accordingly, a new mapping method is presented that is based on topology, in contrast to the mapping methods used so far that are based exclusively on geometry. The most important contribution of this new approach is that due to mapping in topology, an initial guess of the equilibrium position is not needed as part of the solution process. The ease of implementation is also shown in this paper, along with future research that may improve this new idea. Several examples are presented that illustrate the applicability of this new method.

Tall reinforced concrete (RC) building designs must satisfy serviceability stiffness criteria in terms of maximum lateral displacement and interstory drift. It is therefore important to assess accurately the effects of concrete cracking on lateral stiffness of such structures. This study integrates nonlinear cracking analysis methods with a powerful optimization technique and presents an effective numerical approach for the stiffness-based optimum design of tall RC buildings under service loads. A probability-based effective stiffness method is employed to identify cracked members and to modify their effective cracked stiffness. Iterative procedures are necessary for the serviceability analysis of tall RC buildings to determine their nonlinear stiffness characteristics due to concrete cracking. Design optimization based on a rigorously derived optimality criteria approach involves minimizing the cost of RC structures while satisfying the top and multiple interstory drift constraints along with member sizing requirements. A framework example is presented to illustrate the applicability and efficiency of this proposed optimal design tool. Discussions about the effects of concrete cracking on the optimization results are also included.

The main objective of a bridge manager is to find the best maintenance plan for a group of bridges over a prescribed time horizon. The bridge manager usually faces conflicting objectives, as maintenance plans resulting in safer and less deteriorated structures also lead to higher costs. In general, the problem is posed as a deterministic single-objective optimization where cost is minimized keeping performance above predefined thresholds. However, single-objective optimization results in only one optimal solution that does not provide the advantages of considering other objectives and constraints. In addition, the effects of uncertainties are not taken into account or are included in a very simplified way. The bridge manager obtains, in this way, only one deterministic optimum maintenance plan, and not a set of different probabilistic maintenance solutions from which the best, for each particular situation, can be chosen. In this paper, a full probabilistic multiobjective approach to bridge maintenance considering single maintenance types is developed. This approach is based on the latest developments in bridge management by considering probabilistic continuous performance indicators and probabilistically defined objectives and constraints. The problem is solved using multiobjective genetic algorithms and a Latin hypercube sampling technique. Multiobjective applications to existing reinforced concrete bridge components under probabilistic deterioration and probabilistic-defined single maintenance types are presented and discussed.