Journal of Structural Engineering

Corrosion affects the sustainability of steel structures, especially those with improper maintenance and those exposed directly to the atmosphere and seashore environments. Corrosion-related accidents have been reported frequently recently; therefore, periodically assessing the structural health condition of steel structures is crucial. Clarifying the residual strengths of corroded steel structures with moderate to severe degrees of corrosion is important. Here, the uniaxial compressive strength of corroded steel angles and channels was investigated through experiments and nonlinear finite-element analyses. The behavior of these corroded specimens was found to depend strongly on the degree of corrosion, and had combined failure modes of global flexural buckling, local buckling, and cross-sectional yielding. The failure mode of the corroded steel specimens that largely behaved in a complex manner was examined. The relationship between the ultimate strength and degree of corrosion, and the applicability of a traditional global flexural buckling strength equation using the cross-sectional properties, were analyzed for strength evaluation. The strength equation provided relatively good strength estimates for lightly to moderately corroded specimens; however, it became less applicable for severely corroded specimens, possibly owing to the local buckling interaction. An empirical strength equation that reflects the trend of the experimental results was developed by modifying the traditional equation.

In this paper, three precast concrete (PC) frames and one cast-in-situ reinforced-concrete (RC) frame were cast and tested to investigate the load-resisting mechanisms of emulative PC frames with various reinforcing details to resist progressive collapse. In the beams of PC frames, the top reinforcement was continuous without curtailment while the bottom reinforcement had different anchorage strength. Test results indicated that, in the event of middle column removal, similar to RC frame, beam action, compressive arch action (CAA), and tensile catenary action (TCA) could be developed sequentially in PC frames with emulative connections, PC frames with sufficient anchorage strength or additional bottom U-shaped bars passing through the middle joint could obtain similar level of CAA capacity as RC frame. However, they may achieve relatively lower TCA capacity due to higher bond strength between the top reinforcement and cast-in-situ topping layer in beams, owing to higher concrete strength in the topping layer, resulting in earlier fracture of the beam top reinforcements. Conversely, PC frames with insufficient anchorage could achieve comparable TCA capacity as RC frame. However, their CAA capacity was less than that of RC frames due to pulling-out failure of bottom reinforcements, preventing further development of strain hardening at beam action and CAA stages. Based on test results and analytical studies, it was found that, similar to RC frames, PC frames with emulative connections could provide sufficient rotational capacity to ensure development of tie-force as required by the design guidelines.

The focus of this paper is on the probabilistic estimation of the buckling capacity of single-bolted members from plain or lipped angle sections with stochastic geometric imperfections. A joint experimental-stochastic mechanics approach is adopted, employing in-house imperfection measurements of angle members in combination with detailed numerical models. Different slenderness values, plain and lipped angle sections, as well as single-brace or X-bracing diagonals are investigated in all cases accounting for the single-bolt connection. The member buckling loads are obtained via numerical analyses considering geometric and material nonlinearities with initial imperfections. The random variables are the geometric imperfections, the material properties, and the lateral load (wind pressure) on the member. Quatro-variate single-dimensional stochastic processes (the spectral representation method in connection with the method of separation) are used for the modeling of the geometric imperfections. It is shown that the influence of imperfections for typical lattice tower angle members is 3–6 times lower than the influence of material properties and lateral loading. All in all, current EU and US design provisions are found to be mostly conservative for the design of such members, while the use of equivalent imperfections in a numerical model can provide a more rational safety margin.

The fire resistance and residual bearing capacity of prestressed concrete (PC) beams after fire exposure are very important to the safety of engineering applications. This study performed experimental investigations and theoretical calculations of the fire resistance of PC T-beams subjected to a standard fire. Effects of fire exposure time, steel strand location, and prestress level on failure mode, ductility, residual bending capacity, and residual stiffness of PC T-beams were investigated. The bending working mechanism of PC T-beams after exposure to the standard fire was determined. With increased fire exposure time, the ductility and bending stiffness decreased significantly and the failure mode changed. However, because of catenary action, extra vertical force between the end support of specimens and steel strands increased the ultimate bending capacity of fire-damaged PC T-beams. Multilayer steel strands with high prestress could delay initial crack occurrence and increase residual bending capacity effectively. However, they have little influence on residual stiffness.

With the recent increased use of precast concrete (PC) structures, their progressive collapse resistance under hazardous conditions, such as explosion and fire, has become a great concern for the structural engineering community. In this study, static push-down tests were performed on eight PC beam-column substructures, in a column removal scenario due to fire, to investigate their progressive collapse resistance. The test specimens were classified into four groups, and static loading was applied to them under and after fire in a specially designed hybrid heating furnace. The test parameters were the wet-connection details in PC beam-column joints and the timing of high temperature. Structural performance and failure modes were evaluated, including thermal responses, load-displacement relationships, temperature–axial force relationships, and beam moment–axial force relationships. The test results showed that in the joint specimens using a lap splice connection and/or at high temperature, insufficient compressive arch action (CAA) and catenary action (CTA) developed.

In this study, the behavior of rectangular hollow-section (RHS) X-joints in compression is investigated, with a focus on the failure mode of chord sidewall failure, which is more likely to occur when the brace-to-chord width ratio is close to 1.0. For joints with a width ratio of 1.0 (or full-width joints), the test-backed numerical analysis in this study clearly indicated that sidesway instability could readily occur even if sufficient out-of-plane restraint is provided. The sidesway instability was found to considerably impair the ultimate strength of full-width joints. A new borderline width ratio is proposed, beyond which the chord face plastification and chord sidewall failure limit states start to interact and should be considered simultaneously in the joint design. This investigation was motivated by a previous experimental observation, wherein the failure mode of the tested joints with a borderline width ratio of 0.85 as per current design standards was essentially the less ductile chord sidewall buckling observed in full-width joints. Based on simple mechanics, an analytical and more rational expression for the borderline width ratio is derived and validated in this study. After existing formulas for the chord sidewall strength were thoroughly reviewed and all the findings and developments were collated, an improved design recommendation that can cover high-strength steels whose yield stress is as high as 700 MPa is suggested for RHS X-joints under brace axial compression.

Space trusses are extensively used to construct large free spans in roofs. In many countries, connections in such space trusses are made with tubes linked by typical space-truss connections. Typical nodes are made with the superposition of flattened tube ends significantly reducing the strength of such space trusses. This paper presents the use of natural sisal fiber and the reuse of recyclable tires to produce spacers to correct such typical nodes. The choice of those new materials reflects the growing interest in recycling, reducing, and reusing usable waste. There is increasing global environmental awareness of and social concern with the high rate of petroleum resource depletion as in tire manufacture. Moreover, the new environmental and sustainability regulations in engineering arouse interest in new and natural materials like sisal fibers. Therefore, in this paper, two new spacers are presented as an appropriate choice to reduce the eccentricity of typical connections in space trusses. The results of experimental and numerical tests show their efficiency in reducing the eccentricities of typical nodes, increasing the resistance capacity of space trusses with low cost materials. Finite-element (FE) results are compared with experimental results validating the advantages of using these new spacers in typical connections in space-truss nodes.

Steel-concrete composite columns are strong and efficient structural members. However, their strength is not consistently recognized within design standards. In particular, current provisions regarding the strength of composite columns under combined axial compression and biaxial bending are overly simplistic and conservative. This paper presents a study of the biaxial behavior of square and rectangular, filled and encased composite columns and methods of evaluating their strength. Analyses of composite cross sections confirm the conservative nature of current design provisions and form the basis for modified strength equations that better capture the shape of the three-dimensional interaction surface. Analyses of composite columns confirm that the proposed design equations are suitable for use within the direct analysis method for evaluating members with length effects. The proposed design equations are further validated against published experimental results. This paper provides key insights on the behavior of composite columns subjected to axial compression and biaxial bending and offers an improved yet practical method of evaluating strength under these conditions that will enable more efficient designs.

While the tensile performance of high-performance fiber-reinforced cementitious composites (HPFRCC) has been extensively studied, the crushing behavior is less understood. Notably, crushing is an important load-reduction mechanism for reinforced HPFRCC flexural members that fail in a ductile mode, i.e., failure after gradual strain hardening of the steel reinforcement accompanied by gradual HPFRCC crushing. This study first investigates the crushing behavior of HPFRCC flexural members through experimental testing of two reinforced HPFRCC beams. The experimental program includes two types of HPFRCC materials: engineered cementitious composites (ECC) and ultra-high performance concrete (UHPC). The test results show that both ECC and UHPC gradually soften in compression after the initiation of crushing, which is in contrast to the more brittle crushing behavior typically observed in conventional concrete. In addition to the experimental investigation, a new HPFRCC compression model is implemented in a two-dimensional finite-element analysis to simulate the gradual compression softening behavior in reinforced HPFRCC flexural members. Different modeling strategies are compared and evaluated. Results show that the proposed model with an initial material flaw, the new compression model, and a hybrid-rotating/fixed-crack model best predict the reinforced HPFRCC structural performance, especially the failure mode and drift capacity.

In the design, fabrication, and erection of grid shells, a major challenge is the nodal connector between members. Designers typically select a structure’s form and then design the nodal connectors to meet geometric and structural demands. However, this can lead to complicated connections that are difficult and expensive to fabricate. Each connector is also often unique. To address these challenges, this paper investigates a new approach in which a novel modular connector is designed for ease of fabrication and erection, and then structural forms are developed that use the connector repeatedly to join wide flange steel members via splice connections in double shear. This approach modularizes the nodal connector, which is a prefabricated, steel connector with starter segments that include webs and flanges. The flanges and webs of the modular connector and the members are joined independently, thereby achieving a moment-resisting connection. This facilitates trusslike, membranelike, or beamlike behavior and allows loads to be redistributed in the case of sudden member loss or replacement, thereby providing enhanced resiliency. Variability in form is achieved by bending the flange splice plates. This paper investigates the modular connector for free-form undulating grid shells and for rational structural forms developed through a proposed form-finding methodology. The proposed methodology relies on thrust network analysis coupled with geometric and structural constraints. The promise of the modular connector and the proposed methodology is demonstrated through finite-element numerical analyses.

In moderate-seismic regions, cost-effective steel building design solutions such as the $R=3$ and ordinary concentrically braced frame (OCBF) systems do not consistently provide reliable life-safety protection. The collapse performance behaviors of these systems are not thoroughly substantiated by experimental or historical evidence. Thus, a numerical study consisting of 2 conventional and 216 parameterized variations of a prototype seismic force–resisting system (SFRS) was developed to (1) investigate low-ductility braced frame failure mechanisms and collapse performance capabilities; (2) quantify the influences of key design parameters on probabilistic collapse capacity; and (3) provide the basis for development of a robust and socioeconomically viable design alternative for low-ductility concentrically braced frame (CBF) systems. Collapse probabilities were assessed through numerical simulations of ground motion excitations using incremental dynamic analysis (IDA), and variations in collapse probabilities were quantified with respect to five design parameters using an ANOVA model. The results indicate that the collapse probabilities of low-ductility CBF systems can be substantially reduced through design parameters that promote favorable failure hierarchies and provide deliberately engineered reserve capacity.

A probabilistic calibration for traditional deterministic stress-strain models of square confined concrete columns was conducted based on the proposed probabilistic stress-strain model and a large number of experimental data. The probabilistic models for both peak stress and peak strain (strain corresponding to peak stress) of confined normal-strength concrete (NSC) were established first based on the Bayesian theory and the Markov chain Monte Carlo method. Then, a probabilistic stress-strain model of confined NSC was established based on the proposed probabilistic models for peak stress and peak strain. Finally, the confidence level and computational accuracy of four typical deterministic stress-train models of confined NSC were calibrated based on the proposed probabilistic models and a large amount of experimental data. The proposed probabilistic models not only describe the probabilistic characteristics of peak stress, peak strain, and the stress-strain curve, but also provide an efficient approach to calibrate the confidence level and computational accuracy of traditional deterministic models.

Reinforced masonry buildings predominantly are partially grouted in areas of low or moderate seismicity in North America. The walls in such structures typically contain widely spaced separately grouted vertical reinforced cells and bond beams, making such walls prone to brittle shear-dominated behavior. This paper assessed the effectiveness of a new design detail which uses side-by-side vertical reinforced cells to improve the seismic performance of partially grouted masonry (PGM) wall structures. A numerical study was conducted with nonlinear finite-element models to understand the influence of the new design detail on the behavior of wall segments by using data from previous quasi-static tests. A full-scale single-story PGM wall structure was tested on a shake table to assess the influence of the new design detail in the performance of a building system. The test results were supplemented with finite-element analyses. The numerical and experimental results showed that the use of side-by-side reinforced cells can enhance the strength and ductility of PGM structures.

Robustness assessment is an important component for performance-based progressive collapse design. However, existing methods either do not consider the cascading failure feature of progress collapse, or fail to recognize the randomness in material, geometrical and loading parameters. This paper presents a novel robustness assessment methodology for progressive collapse design of reinforced concrete frames. The proposed methodology includes several novelties: First, it uses a new risk-based robustness index recently developed by the authors. The index quantifies the whole spectrum of risk caused by initiating hazardous events. Second, it includes a unique directional simulation technique, making probabilistic nonlinear pushdown analysis a computationally affordable task. Finally, the assessment can assist in determining if an enhancement design is warranted for such a low-probability-high-consequence event. The study examined four different frame designs to evaluate the effectiveness of seismic and progressive collapse design provisions. The Alternate Path Method (APM) was shown to improve structural robustness significantly, although achieved with considerable additional cost. Ductility designed for seismic loading was also shown to be beneficial for structural robustness against progressive collapse.

Tall residential RC shear wall buildings (RCSW), which are predominant in Metro Vancouver, have the potential to experience large magnitude earthquakes generated by the Cascadia Subduction Zone (CSZ). Furthermore, the region lies above the Georgia sedimentary basin, which can amplify the intensity of ground motions at medium to long periods and the resulting damage in tall structures. This study provides insights into the effects of the Georgia sedimentary basin amplification on (1) spectral accelerations associated with magnitude 9 (M9) CSZ earthquakes, (2) resulting force- and deformation-controlled actions in modern tall RCSW buildings, and (3) ensuing earthquake-induced repair costs and times. To this end, we leveraged a suite of physics-based ground motion simulations of a range of M9 CSZ earthquake scenarios, which explicitly consider basin effects, and benchmarked these scenarios against a range of seismic hazard intensities, which neglects basin effects. While the M9 simulations have an estimated 500-year return period, at deep basin sites their spectra exceed the 2,475-year hazard in the 1–3 s period range. Nonlinear dynamic analysis results under probabilistic seismic hazard estimates result in negligible collapse risk. In contrast, collapse risk conditioned on the occurrence of the M9 motions results in probabilities as high as 15%. Additionally, seismic demands from the M9 simulations at deep basin sites result in earthquake-induced repair costs and times that exceed those associated with the 2,475-year hazard level.