Journal of Structural Engineering

The initial rotational stiffness of connections is important for the design of semirigid frames. However, most current studies on steel beam to concrete-filled steel tube column connections with bidirectional bolts are based on experimental tests, and theoretical analysis and numerical analysis are rarely reported. As a result, there is no suitable analytical model for calculating the initial stiffness of the connection. Based on the component method, this paper proposes an analytical model to predict the initial stiffness of the connection. It is considered that the connection rotation is mainly induced by deformations of the endplate in bending, column flange in bending, bolts in tension, and panel zone in shear. Moreover, the effects of the endplate in bidirectional bending and bolt pretension are taken into consideration. Then, the prediction results based on the proposed analytical model are compared with experimental results to verify its accuracy, and comparison results indicate that the proposed analytical model can predict the initial rotational stiffness of steel beam to concrete-filled steel tube column connection well. In addition, bolt diameter and endplate thickness are the most influential parameters that affect the initial stiffness of the connection. It also provides a way for such connections to be designed as rigid connections. Finally, the proposed analytical model can be applied with good precision in elastic analysis and serviceability calculations in the design of semirigid steel-concrete composite frames. It can be applied to four types of connections: stiffened extended endplate connections, nonstiffened extended endplate connections, flush endplate connections, and T-stub connections. The proposed analytical model saves substantial resources and workload in experiments and simulations.

Corrugated steel plate shear wall (CoSPSW) is a lateral load–resisting system in which corrugated infill steel wall panels are embedded inside a steel boundary frame. Compared to flat steel plate shear walls (SPSWs), elastic buckling capacity and lateral stiffness could be enhanced considerably, and gravity loads could be avoided when the load is perpendicular to the rib, or resisted when the load is parallel to the rib, which solves the long-lasting problem of flat wall buckling under gravity loads during construction. Cyclic quasi-static tests were conducted on three, 1/3-scale, 2-story, single-bay CoSPSW specimens with different corrugation orientation and configuration. All specimens showed highly ductile behavior and stable cyclic postbuckling performance. Compared to the SPSW specimen, CoSPSW specimens had much higher lateral stiffness and elastic buckling capacity, with less pinching in the hysteric curves. Different from the tension field action mechanism in SPSW, the lateral load–resisting mechanism in CoSPSWs was shear yielding, or inelastic shear buckling, depending on the corrugation configuration. The experimental results and their implication on seismic design are summarized and discussed.

A number of experimental and analytical studies have been conducted on the axial compressive behavior of square concrete-filled steel tubular (CFST) columns, but there still exist several controversies on this issue because the loads sustained by the concrete infill and the steel tube cannot be accurately measured in a conventional axial loading test. In this study, an innovative test method was devised to directly measure the load components of square CFST columns under axial compression. Five specimens with different width-to-thickness ratios were fabricated and tested. The factors that may affect the compressive strength of concrete in square CFST columns were investigated, and it was found that the difference between the compressive strength of concrete in CFST columns and the corresponding cylinder strength was small and within the commonly accepted ranges. The measured compressive strengths of the steel tubes were compared to the available empirical formulas. It was determined that the ultimate strength of the steel tube can be reasonably estimated, but more research is needed to fully understand the post-local-buckling behavior of the steel tube and the effects of various factors. Design recommendations were proposed for the axial load capacity of square CFST columns. The existing stress-strain models for the concrete infill and the steel tube were assessed using the measured stress-strain relationships, and more credible stress-strain models were developed.

This study investigates the vortex-induced vibration (VIV) behavior of a twin-box girder bridge by means of aerodynamic sectional wind tunnel test and particle image velocimetry (PIV) measurements. The effect of grid plates on suppressing the VIV of twin-box girder model is examined and the influence of four design parameters of grid plates [porosity, flat plate width (FPW) ratio, composition type, and installation position] is studied. The primary causes of VIV and the suppression mechanism of grid plates are discussed in detail. It is found that torsional VIV is more vulnerable to the change in wind attack angle than is vertical VIV. The installation of grid plates noticeably suppresses the VIV of test model and its effect depends on the variation of different design parameters. For the porosity and FPW ratio, there is an optimal range in which the improvement of VIV suppression is more significant; the optimal value of porosity is about 42%–67%, and the optimal value of FPW ratio is about 0.042–0.167. Moreover, the uniform distribution of grid plates is more preferable in terms of suppressing VIV than is nonuniform distribution, whereas the installation of grid plates on the upper side leads to better performance of VIV suppression than does installation on the lower side. The primary cause of VIV of the twin-box girder is closely related to the formation of large-scale vortex shedding at the tail of the upstream box girder. The generation of large-scale vortex can be eliminated by appropriate selection of the design parameters of grid plates.

Base isolation is an effective method for mitigating seismic hazards and improving seismic performance under design-level ground motions. Previous studies have typically focused on comparing the performance of isolated and fixed-base buildings under design level or maximum considered level earthquakes without modeling the failure of the isolation bearings components. However, it is also important to include the performance of the isolation system under extreme conditions. A numerical model which explicitly includes both impact and uplift behavior of the sliding bearings as well as degrading behavior of the superstructure is used to investigate the collapse risk of the various friction pendulum isolated moment-resisting and concentrically braced frame designs. It is found that the stiffness of the superstructure has a large influence on the overall collapse risk. For flexible moment-resisting frames, increasing the strength is beneficial to improving the safety margin between impact and system-level failure. However, for stiff concentrically braced frames, because of their high stiffness, impact with the sliding bearing rim imposes a large ductility demand on the superstructure regardless of its strength, resulting in an unacceptable probability of collapse.

The use of protective barriers is one of the most common approaches to protect buildings and their occupants against blast and vehicle impacts. They increase the stand-off distance between the explosive source and the building. However, the protection capabilities of barriers with openings have not yet been thoroughly studied. The present paper discusses the shock wave attenuation effect of protective barriers made of steel posts with a hollow cross section. In the experiments, the steel posts are located at a distance of 5 m to the building to be protected. Prior to the experiments, numerical models were developed to predict the blast loads numerically. Overpressure-time history measurements (side-on and reflected) were made at various distances in front of and behind the barrier. The experimental data were used to, for example, validate the numerical models. The experimental and numerical results showed that barriers can reduce the blast loads relative to the scenario in which no barriers were present. Considerable reductions in peak side-on and reflected overpressure and impulse were observed behind the barriers. Furthermore, after validation, parametric studies are carried out to investigate the influence of further parameters on the overpressure reduction behind the barriers, that is, the number of posts or the spacing between posts, the cross-sectional shapes of posts, and the arrangement of posts (single-layer or multilayer, aligned or staggered). These studies showed that a barrier without openings is not always necessary to offer the desired protection because barriers with openings can also show satisfactory results. Hence, the necessary amount of material (steel in this case) and, thus, the construction cost can be considerably reduced.

This study explores a geometric method of structural morphogenesis, referred to here as the quasi-mechanism (QM) method because it is based on the self-adapting function of mechanism systems. First, a net-shaped mechanism system is modeled by adopting B-spline curves. Subsequently, an equation of shape is established to determine the tendency of shape transformation under the condition of constraining the length of each cable. This equation is solved using the generalized inverse matrix theory and the gradient of potential energy increment with shape transformation. Next, an iterative process is formed to determine the final shape of the system, which corresponds to an optimized structural shape featuring a predominant axial force and small bending moment under a specific loading case. Finally, the new structural shapes generated by the QM method illustrate its validity and characteristics.

Major earthquakes in urban areas often lead to building fires. Such earthquakes frequently damage buildings’ water sprinkler systems and diminish or strain firefighting capabilities. In such scenarios, buildings get exposed to fire for a long period of time, resulting in damage of spray-on-fire resistive materials. Consequently, steel frame temperature may reach as high as the maximum fire temperature, which subsequently cools slowly to ambient temperature. If the building frame does not deform severely after such a fire event, it is usually rehabilitated for continued occupation. The performance of such a fire-exposed steel building during a future earthquake is not known. This study investigates the seismic performance of a fire-exposed steel frame by performing finite-element analyses incorporating fire-exposed steel material properties. The simulation responses demonstrate vulnerability of fire-exposed steel buildings. A novel but startling observation made is that under seismic loading, a fire-damaged steel frame may form a soft-story mechanism at the story of fire exposure because of plastic hinge formation in the column instead of in the beams.

Structural health monitoring (SHM) is a method for determining the structural integrity of civil infrastructure elements as a basis for maintenance and repair protocols. This monitoring depends on collecting structural response data from sensors installed on the structure due to in-service excitations. The installation additionally requires access to structural elements, power, and communication. New methods for remote measurement of displacements using video cameras could greatly simplify the process of instrumentation, making SHM much more attainable for many structures. This paper presents the remote camera measurement of the motions of the World War I Memorial Bridge in Portsmouth, New Hampshire, a vertical-lift bridge, from a distance of over 80 m. Vibration frequencies and mode shapes of the bridge are identified by measuring the displacements due to the lift span impact. Displacement of the bridge due to in-service traffic is also measured. Measured signals are compared with those from accelerometers and strain gauges installed on the bridge, and identified characteristics of the bridge are compared with a finite-element model for verification. Results show the potential of applying video cameras to measure and visualize vibrations of structures in SHM.

A new relationship was developed for estimating fire resistance ratings of gypsum board protected steel columns with high load ratios. The proposed formula can be used to adjust the limiting steel temperature, the commonly used 1,000°F (538°C) by the US standards, for steel columns with high load ratios. A two-dimensional finite-element analysis (2D FEA) heat transfer model, using Abaqus, was established to analyze the heat transfer of gypsum board protected steel columns exposed to the ASTM standard E119 temperature rising history. The numerical model was validated against available fire resistance ratings of protected steel columns, full-scale column fire resistance tests, a wall assembly fire test, and a column test that included a different range of steel temperatures. Results were also compared with those by SAFIR, one of the main available software packages for analysis of structures in fire. Steel temperature histories were used to extract fire endurances, and the extracted fire endurances were then used to construct a formula for predicting fire endurance for gypsum board protected steel columns at critical or limiting temperatures lower than 1,000°F (538°C).

Bond-slip characteristics of slightly corroded (less than 2% mass loss) reinforcing steel bars embedded in concrete were investigated with pull-out tests conducted after exposure to high temperature and subsequent cooling. Twenty-five scenarios consisting of five corrosion levels (0.0%, 0.5%, 1.0%, 1.5%, and 2.0% corrosion loss) and five exposed temperatures (20°C, 200°C, 400°C, 600°C, and 800°C) were tested. The results indicate that the slight corrosion of the reinforcement not only affects the bond performance of concrete and steel bars but also influences their reaction to elevated temperature before the exposure temperature exceeds 400°C. The effect of slight corrosion on bond-mechanics behavior was eliminated by the dramatic decrease in concrete strength and significantly different thermal expansion between concrete and steel as the exposure temperature reached 600°C.

This paper presents the extension of controlled rocking technology to steel bridge piers through analytical expression and finite-element (FE) simulation. As an outcome of the rocking behavior, the seismic damage is prevented due to reduced flexural stresses in the columns. However, local buckling can happen if the column wall thickness is too thin, which has detrimental impacts, including the loss of self-centering ability and reduced lateral load/deformation capacity. A simple analytical method is proposed to predict the monotonic rocking response for preliminary design purposes. When using more-detailed models and FE analysis, it is shown that localized inelastic deformations of the column can occur upon rocking and the simple force distribution at the column base can cause an overestimation of lateral load capacity. The use of a base plate can lead to a higher lateral load capacity and less damage to the column by improving the stress distribution at the base of the column. To account for the base plate, previously proposed modified monolithic beam analogy (MBA) was expanded in this study, referenced as extended MBA (EMBA) to predict the rocking column lateral load-displacement response. An optimized design can be achieved with a lighter cross section in the upper part of the column where longitudinal straining is limited. Different axially yielding elements comprised of tension-only, tension-compression, and buckling-restrained energy dissipators (EDs) are investigated. For EDs with comparable force capacities, the study indicates that energy dissipation is increased from the former to the latter dissipator type, while the lateral load capacity of the system remains almost the same. The proposed pier exhibits recentering capability, high ductility, and stable hysteretic response with the majority of damage confined within external sacrificial elements.

A method is presented for calculating the uncertainty associated with the estimation of peak pressure coefficients from wind tunnel test records of various lengths and how this uncertainty influences design wind effects. The proposed method is applicable to any type of structure and any type of civil engineering aerodynamic testing facility, including large-scale facilities. As an example of the application of the method, an investigation is presented of time series belonging to five categories of pressure coefficients implicit in Chapter 27 of the ASCE 7-10 Standard. The results of the investigation show that, for typical civil engineering wind tunnels, estimated design wind effects based on tests with durations as low as 10 s, corresponding to prototype durations of less than 6 min, are larger than their counterparts based on tests with 100 s duration by only approximately 5%. The proposed method provides useful indications on minimum lengths of pressure records to be measured in wind tunnels.