Journal of Structural Engineering

Cantilevered steel sign structures, commonly used to support freestanding signs, are flexible, have low damping, and can be prone to fatigue-type failure as a result of wind-induced vibration. A sleeve connection, involving horizontal ring plates with two-sided fillet welds welded to the upper pipe and slot welds to connect the lower ring plates to the lower pipe, is commonly used to splice the upper and lower pipes of different diameters. Although the majority of these structures have performed well in long-term use, some structures have been damaged or destroyed as a result of cracking at the weld toe of the sleeve connections. A testing program was developed to evaluate the relative fatigue life of conventional and alternative connection details. Testing demonstrated that conventional welded connections had a short fatigue life. A revised sleeve connection detail incorporating a one-sided fillet weld detail at the critical joint was effective in enhancing the fatigue performance. Replacing slot welds by cement grouting the gap between two pipes significantly increased the fatigue life. Using a welded cone to provide a smooth transition between the pipes also showed improved performance. A tapered slip-joint connection that required no welded joints between the pipe sections provided the best fatigue performance.

Shear walls provide the lateral resistance needed for light-frame wood structures to withstand earthquake and wind loads. When sheathed with wooden structural panels, shear walls can be strong, stiff, and ductile. This is a study on the effect of wood species and drying temperature of veneer on the suitability of plywood for use in shear walls resisting earthquake loads. The highest lateral nail strength values were obtained from plywood panels manufactured from black pine veneers dried at 160°C. Group C (black pine) showed the highest maximum load values and the greatest displacement at ultimate load, whereas Group A (Scots pine) showed the lowest maximum load values and the least displacement at ultimate load. The stiffness values (2.38, 2.52, and 2.28 for Groups C1, C2, and C3, respectively) in Group C were higher than those of the other groups. The results exceeded the values for standards described in National Design Specification for Wood Construction and ISO 16670 and also met the values in American Plywood Association Form L350G for diaphragms and shear walls. Shear strength mean values obtained from the samples of all plywood panels were above the limit value ($1.0\mathrm{N}/{\mathrm{mm}}^2$) indicated in the EN 314-2 standard. The highest shear strength mean value was obtained from Group C ($1.86\mathrm{N}/{\mathrm{mm}}^2$). It was also found that the bending strength of plywood panels was higher than the minimum values for structural purpose plywood panels ($40\mathrm{N}/{\mathrm{mm}}^2$) indicated in Deutsches Institut für Normung (DIN) 68705-3. The bending strength values (above $80\mathrm{N}/{\mathrm{mm}}^2$) of Group C exceeded twice the standard. The plywood panels were all manufactured from softwood species growing in Turkey, because producing plywood from softwood may prove to be a new opportunity for sustainable forestry in Turkey.

This paper presents a comprehensive experimental study of the time-dependent creep and shrinkage behavior of a simply supported steel-concrete composite beam that is curved in its plan; it is a companion to the first paper that presented a numerical model for spatially curved members for which a beam curved in plan is a limiting case. The full-scale beam was tested under sustained uniformly distributed loading for approximately 250 days; its time-dependent deformations and strains were monitored throughout the period of loading. Separate companion concrete specimens were tested under the same ambient conditions as the test beam to determine the creep and shrinkage characteristics of the concrete component of the beam. The test observations show that the creep and shrinkage behavior of the concrete component has a significant effect on the long-term response of curved composite beams. The experiment also provides benchmark data to test the validity of theoretical models and shows that the developed numerical technique is able to predict the deflections of the test beam acurately; hence, it is able to provide a reliable computational model from which to formulate design guidance.

This paper develops a numerical formulation for the nonlinear time-dependent analysis of steel-concrete composite members that are curved arbitrarily in space, which includes the effects of concrete shrinkage, creep, and geometric nonlinearity. This formulation is applicable to the analysis of composite arches and composite beams curved in plan, representing the limiting cases of members that are vertically and horizontally curved. The flexibility of the shear connection at the interface surface between the steel girder and the concrete deck is taken into consideration in the formulation. For an accurate serviceability limit state analysis of composite curved members, it is essential to include the shrinkage and creep response of the concrete component in the analysis. To also include the effects of geometric nonlinearity, a step-by-step incremental iterative solution procedure is adopted. Comparisons of the numerical solutions with those based on much less efficient and tractable viscoelastic ABAQUS shell element models, and with available experimental results, verify the accuracy of the computational formulation that is developed. Examples are chosen to illustrate the effects of partial interaction and initial curvature on the time-dependent behavior of spatially curved composite beams.

Few studies on the anchorage of reinforcing bars under the compressive conditions have been undertaken. This paper reports the results of 99 pushout tests done to investigate the compressive bond anchorage properties of 500 MPa steel bars in concrete. The precise slip values have been measured using a laser displacement sensor with high resolution, allowing the complete force-slip curves to be obtained. The influence of concrete strength, bar diameter, concrete cover, embedded length, and transverse reinforcement on the bond properties under compressive conditions is investigated. A new formula for calculating the compressive bond strength for 500 MPa reinforcing bars in concrete is proposed based on the test results.

Cross-laminated timber (CLT) is a growing phenomenon and a recent building solution alternative in timber construction in North America by using massive or solid wood plates as roof, floor, and wall elements. In this paper a variation of the conventional CLT is considered by studying the performance of box-based CLT systems, which refer to box beams with multiple voids. In some loading situations, such as out-of-plane bending, these systems, which can reduce structural weight without significant loss of strength or stiffness, may be structurally efficient and cost competitive. Comprehensive three-dimensional finite-element models, which can be used to analyze the mechanical behavior of such box structures, were developed. Four prototype layups, each having five replicates, were designed, manufactured in-house, and tested under symmetric four-point bending (also known as third-point loadings). The numerical analysis agreed well with experimental data in terms of vertical deflection and flexural rigidity. This paper contributes to the understanding of the structural performance of box-based CLT systems for the commercial and residential applications.

An analytical model to investigate the shear resistance mechanism of a posttensioned precast concrete (PPC) member is proposed. The model is based on the truss mechanism. The compatibility of strains and the equilibrium of stresses of the shear cracked concrete, prestressing steel, and shear reinforcement are applied to the shear model. The proposed truss model consists of three stress zones (zones 1, 2, and 3). Triangle struts of cover concrete subjected to uniaxial compressive stress are defined as zone 1. Biaxial stress zones of diagonally cracked concrete between the longitudinal bar and prestressing steel are defined as zone 2. Zone 3 is defined as the diagonally cracked concrete zone between both compression and tension prestressing steels. The model considers the bond characteristics of prestressing steel. The proposed truss model is useful to predict not only shear strength, but also the shear deformation, tensile stress in shear reinforcement, and failure mode of a PPC member. By comparison of experimental and analytical results, an accuracy of analytical results by the proposed method was verified. The proposed method evaluated experimental results, which are shear strength, shear strain, and tensile stress in shear reinforcement in a good accuracy.

This work aims to develop an axial load capacity equation for doubly symmetric built-up cold-formed sections with a sufficient number of intermediate, symmetrical connections. A numerical parametric study involving a total of 360 different configurations was conducted, and the numerical results were compared with the experimental data and specifications from the American Iron and Steel Institute (AISI). In this process, the axial load capacities and failure modes, which were influenced by out-of-straightness and out-of-flatness, were thoroughly investigated. To address the issues of an unnecessarily complicated AISI specification for doubly symmetric members subject to distortional buckling, a simple and reliable axial load capacity equation was developed based on a regression analysis of a three-dimensional surface fitting and calibration with the experimental data. This proposed equation exhibited good agreement with the numerically simulated and experimentally measured capacities, while simultaneously ensuring safety and efficiency.

The stability of Z purlins subject to combined axial force and biaxial bending due to self-weight (a situation that typically arises during construction) is investigated. Single, isolated purlins as well as purlins with one or more lines of bridging are considered. The purlin can thereby be supported at the ends in various ways: (1) a simple cleat plate connection with two bolts, (2) a semicontinuous connection obtained by lapping the purlin with an adjacent span, and (3) a cleat plate connection with fly-bracing. The beneficial effect of the end restraint provided by each of these different support conditions about both a horizontal and a vertical axis was measured experimentally. The experimental data served as input for (1) detailed finite-element models, and (2) a theoretical buckling analysis of Z-section columns. Based on this work, design guidelines are presented for Z purlins subject to combined axial force and biaxial bending.

In the last two decades, several efforts have been made to monitor the cracking behavior in RC structures. A technique that shows promise is acoustic emission (AE). This paper presents the results of an experimental study aimed at monitoring fracture processes in a large-scale RC shear wall using one of the most important AE parameters, that is, the $b$-value. The specimen was subjected to a displacement controlled reversed cyclic loading. A Gaussian filter is proposed to improve the interpretation of $b$-value data obtained during the test. In addition, a cluster analysis based on the $k$-means is presented to automatically classify the signal into tensile and shear cluster. Finally, a new algorithm called Sifted $b$-value ($\mathrm{S}b$) analysis is introduced to monitor the evolution of each crack mode. The proposed approach is capable to identify the initial yielding and eventually provide an early warning for the planning and implementation of remedial action to the structure at a point at which it is less expensive and invasive than when its structural performance has been seriously compromised.

The effect of corrosion of properly anchored longitudinal reinforcement on the structural behavior of shear-critical RC slender beams was experimentally investigated. A total of 10 medium-scale reinforced concrete beams were constructed. The beams measured 150 mm wide, 350 mm deep, and 2,400 mm in length. The test variables included corrosion levels (0, 2.5, 5, and 7.5%), existence of stirrups, and fiber-reinforced polymer (FRP) repair. Eight beams were subjected to artificial corrosion and two beams acted as control uncorroded beams. Following the corrosion phase, all beams were tested to failure in three-point bending. The test results revealed that corrosion of properly anchored longitudinal steel reinforcement does not have any adverse effect on the behavior of shear-critical RC slender beams. Corrosion changed the load transfer mechanism to a pure arch action and as a result the load-carrying capacity of the beam was improved. A simple analysis procedure was proposed to predict the failure load of such beams and the predicted results correlated very well with the experimental results.

Concrete-filled tubes (CFTs) have been used in civil engineering practice as piles, caissons, columns, and bridge piers. Relative to conventional structural steel and reinforced concrete components, CFTs have several advantages. The steel tube serves as both reinforcement and formwork, eliminating the need for both, and provides large tensile and compressive capacities; the concrete fill restrains buckling of the steel tube, which increases the strength, stiffness, and deformability of the section. In some cases, internal reinforcement is used to enhance the strength and facilitate connection to adjacent members. Although these properties are well accepted, the use of CFTs in practice is awkward because design provisions among codes vary significantly and previous research has not considered internal reinforcement. An analytical research study was undertaken to evaluate and improve design provisions for CFTs with and without internal reinforcement under combined axial load and bending. A continuum model was developed to simulate prior test results subjected to combined loading and the validated model was used to investigate the strength and inelastic performance of CFTs under combined loading. Current design provisions for CFTs were evaluated using the results of these finite-element analysis and previous test results. The comparisons indicate that current design approach provides good prediction of CFT capacity subjected only to bending or axial demands, but current provisions provide conservative values for the CFTs under general combined loading. An alternative $P\text{-}M$ interaction curve for CFTs was proposed.

Brillouin optical time domain reflectometry or analysis (BOTDR/A) is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. Although the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of approximately 1 m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR/A readings, and hence, the exact nature of cracking might not be resolved. This study suggests different crack indicators and analytically and experimentally examines their correlations with BOTDR/A readings of damaged RC beams. The analytical part entails a finite-element based statistical analysis of hundreds of cracking cases in fractured RC beams and their effects on the simulated BOTDR/A readings. It is found from the analysis that the increase of curvature measured by BOTDR/A is best correlated with the sum of ratios of crack size to the remaining healthy cross section within 1 m. This finding is supported by an experimental study of a cracked RC beam. The correlation, by itself, is only valid when the increase of curvature is associated with the damage and does not involve a curvature increase as a result of redistribution of moments. This, however, would be the case only in statically determinate beams. To facilitate the use of the correlation for statically indeterminate beams, this paper suggests an iterative algorithm that evaluates the different contributors to the increase of the curvature.

This study contributes to the improvement of capacity models for older-type RC members to be used in the seismic assessment of existing RC structures. A database of experimental tests on RC columns with plain bars is presented. Due to the low bond strength, the deformation capacity of these members is particularly influenced by fixed-end rotation mechanism compared with members with deformed bars. ASCE/SEI 41 provisions on the deformation capacity of older-type RC columns, including later proposed modifications, are reviewed. Provisions for the evaluation of effective stiffness are reviewed, too, and special attention is paid to failure mode classification. The effectiveness of such provisions for columns with plain bars is evaluated through their application to the presented database. Results obtained from the application of the effective stiffness model are illustrated, and possible improvements are discussed. A significant conservatism in the plastic deformation capacity model is observed. Deformation limits could be relaxed while still meeting code safety requirements. The amount of this adjustment for ASCE/SEI 41 provisions on the deformation capacity of older-type RC columns is evaluated.

High-strength adhesives provide an alternative, and potentially more efficient, load-bearing connection to conventional bolted connections in glass structures, but the relative structural performance of these connections has yet to be established, and the accuracy of existing predictive techniques is largely unknown. This paper describes the parametric and experimental investigations undertaken to compare the structural performance of nominally identical bolted and adhesive connections subjected to short duration loads. The paper also reports on the accuracy of existing empirical and numerical techniques for predicting the load-bearing capacity of these connections. The investigations show that the load-bearing capacities of the single-lap and double-lap adhesive connections can exceed that of the double-shear bolted connections, and that failure in the adhesive connections tends to be less catastrophic. The existing empirical methods provide good approximations of the load-bearing capacities of bolted and adhesive connections within the limits of applicability. The numerical strength predictions based on an equivalent stress approach produces the most accurate predictions, but all methods are sensitive to the glass strength parameters selected.

Assessing the stability of individual isolators is an important consideration for the design of seismic isolation systems composed of elastomeric bearings. A key component for the stability assessment is the prediction of the critical load capacity of the individual bearings in the laterally undeformed (service) configuration and at a given lateral displacement (seismic). The current procedure for estimating the critical load capacity of an elastomeric bearing at a given lateral displacement, with a bolted connection detail, uses a ratio of areas to reduce the critical load capacity from that in the laterally undeformed configuration, referred to as the reduced area method. Although the reduced area method provides a simple means for the estimate, it lacks a rigorous theoretical basis and is unable to capture the trends observed from experimental data. In this study, the capability of two analytical models for predicting critical loads and displacements in elastomeric bearings is evaluated by comparison with data from past experimental studies. A global variance-based sensitivity analysis is performed on the analytical model showing the best predictive capability to identify the model parameters to which the model prediction is most sensitive. The results of the sensitivity analysis demonstrate that the model prediction is most sensitive to the properties that control the nonlinear behavior of the rotational spring for lateral displacements greater than approximately 0.6 times bearing diameter/width. This finding suggests that the stability of elastomeric bearings at large lateral displacements is controlled by the transition from the yield moment to the ultimate moment in an individual rubber layers. A modified analytical model is proposed based on the results of this sensitivity analysis. The predictive capability of the more parsimonious modified model is shown to be similar, if not improved, by comparison to the original model.

The hazard function is one of the most used lifetime distribution functions in reliability analysis of components and systems. Although it is extensively used in several scientific disciplines, few applications have been proposed in the field of civil infrastructure systems. In this paper, the hazard function is used to provide optimal inspection/repair lifetime planning for deteriorating structures through an iterative procedure. The proposed approach is based on the definition of a threshold value for the hazard function. Constraints are imposed based on both the maximum allowable expected total cost and minimum allowable effectiveness of each intervention. Uncertainties related to damage detection during inspections and attitudes towards repair are considered. An optimization procedure for determining the best threshold value for the hazard function, with target maximum expected failure time, is proposed. The method is applied to an existing deteriorating bridge deck under corrosion.

This paper describes bending tests at ambient temperature and large-scale fire tests of cross-laminated timber (Xlam) floor panels. Three specimens exposed to standard fire curve were loaded out-of-plane with different levels of uniformly distributed load, and in two cases collapse was reached. Other unloaded panels were protected using different cladding systems with the aim to investigate their thermal behavior. Experimental data obtained from the tests and discussed within the paper includes modulus of elasticity and bending strength at ambient temperature, temperature distribution, charring depth, charring rate, residual cross section, midspan deflection, and time to failure in fire conditions. This data was compared with numerical results obtained by implementing a finite-element model in Abaqus software package for sequential thermal and structural analyses, demonstrating the accuracy of the model. The overall fire performance of the Xlam panels was satisfactory; times to failure of 99 and 110 minutes were found, respectively, for the unprotected and protected panels loaded with 21% of the mean failure load at ambient conditions.

The primary objective of this paper is to study the dynamic responses of a flexible multiple degree-of-freedom structure coupled with the three-dimensional motions of a nonlinear pendulum tuned mass damper (PTMD). The three-dimensional motions consist of both planar and spherical motions of the PTMD. The optimal damper parameters obtained by using the three-dimensional model are compared with those predicted by models in which PTMD motion is linearized to the planar direction. The effect of and sensitivity to frequency and auxiliary damping detuning are considered for various levels of primary to auxiliary mass ratios. The performance of the PTMD is evaluated by using a finite element representation of an actual tower structure equipped with a PTMD, together with the responses obtained by using the high frequency base balance method from a boundary layer wind tunnel. The results are compared for linearized and three-dimensional PTMDs and the effect of directional coupling introduced by the nonlinear three-dimensional PTMD on the response estimates is studied by using the numerical model. Finally, a procedure is presented for conducting a condition assessment of existing PTMDs.

Analytical mode decomposition (AMD) of a time series concerning any preselected bisecting frequency with Hilbert transform has been developed for closely spaced multicomponent signal decomposition. For this class of structures, it is often challenging, if not impossible, to apply empirical mode decomposition. In this study, the instantaneous structural frequencies are directly derived from the decomposed modal responses for systems with single and multiple degrees of freedom with both free and force vibrations, based on AMD combined with Hilbert transform analysis. The results show that the slow varying component of the instantaneous frequency of the signal is approximately equal to the instantaneous frequency of the systems for slowly time varying linear or weakly nonlinear structures. Both numerical simulations and experimental tests show that the proposed method is capable of tracking the frequency variations with high accuracy for time varying linear structures or weakly nonlinear structures.

Recent investigations have demonstrated the ability of semiactive devices to reduce the structural vibration. In this paper, a new device called the semiactive damper actuator (SADA) is introduced, which reduces the vibration response of structures during earthquakes. Numerical simulations are carried out to study the effects and advantages of SADA. Simulation results are presented and the responses of structures equipped with this device are compared with ones equipped with other similar devices. The results show SADA’s ability to reduce the seismic response of structures. SADA is a semiactive type and requires low energy to operate; therefore, it can be used widely to control the seismic response of structures.

A new one-dimensional two-node layered composite beam element that accounts for the bond-slip between reinforcing bars and surrounding concrete is presented for nonlinear analysis of steel/fiber-reinforced polymer (FRP) concrete beams. A layered approach is used not only to represent the nonlinear material property accurately but also to model the bond-slip effect between the reinforcing bars and the concrete. In addition to the typical transverse displacement and rotation at the two nodes of the beam element, additional nodal degrees of freedom are introduced to represent the axial displacements of the reinforcements to account for bond-slip effect. Timoshenko’s beam functions are employed for the displacement shape functions, and shear locking is avoided naturally. The element is validated against numerical examples and demonstrated to be accurate and computationally efficient for the analysis of steel/FRP-reinforced concrete beams with bond-slip.