Journal of Structural Engineering

A model is presented that can predict the load-deformation response of reinforced concrete subjected to reverse-cyclic (seismic) shear. Average strains due to crack displacements are separated from concrete strains according to simple assumptions resulting in a rational model that can account for the two sets of cracks that are open when applied shear reverses direction. Closing cracks are assumed to close as a function of the compression stress applied normal to cracks, while opening cracks open as necessary to maintain compatibility of concrete and reinforcement strains. With the separation of strains due to crack displacements, simple material stress-strain relationships for concrete and reinforcement are sufficient to capture the complexities of reverse-cyclic response. The model accurately predicts underlying mechanisms such as accumulation of plastic strain in reinforcement, which defines the degree of pinching in the hysteretic response of reinforced concrete subjected to reverse-cyclic shear. Concrete shear failures are captured by a limit on ultimate shear strain that depends on the shear strain at first yielding of reinforcement and the ratio of shear stress to concrete strength.

Seismic performance requirements for beam-column joints of earthquake-resistant reinforced concrete (RC) frames are discussed, and the experimental data of RC joints under cyclic loading collected from the literature are analyzed. It is observed that joint shear failure under cyclic loading is characterized by significant inelastic joint shear deformation. Joint shear strength should thus be formulated by limiting the influence of joint shear deformation on the seismic performance of RC frames. It is noticed that joint transverse reinforcement does not have significant influence on joint shear deformation and bond deterioration in the joints but may have significant influence on joint axial capacity under cyclic loading. Hence, the requirement for joint transverse reinforcement may be formulated by keeping the joint axial capacity not lower than the column axial capacity under seismic action. The influence of bond deterioration in joints on the seismic performance of RC frames and the anchorage requirement for beam reinforcement in joints are analyzed and discussed.

Six full-scale nonseismically detailed reinforced concrete interior beam-wide column joints were tested to investigate the seismic behavior of the joints. Axial compression loads varying from zero to high magnitude, as well as quasi-static cyclic loading simulating earthquake actions were applied. The overall performance of each test assembly was examined in terms of lateral load capacity, drift, stiffness, energy dissipation capacity, and joint shear strength. Three levels of axial compressive column load were investigated to determine how this variable might influence the performance of the joint. The tests also explored the effects of centerline eccentricity on the performance of interior beam-wide column joints subjected to earthquake loading. All the specimens failed at the joint panel with gradual strength deterioration, low attainment of structural stiffness, and bond degradation. The low attainment of stiffness and strength was attributed to the bond deterioration of the longitudinal bars through the joint core. It is concluded that special reinforced concrete interior beam-wide column joints with nonseismic design and detailing, could possess the inherent ductility for an adequate response to unexpected moderate earthquakes.

An experimental study was performed to investigate the structural capacity of steel plate walls with various infill plate designs. Five three-story steel plate shear walls with thin infill plates were tested. The parameters for this test were the connection method between the boundary frame and the infill plate (welded connection versus bolted connection), length of the welded connection (full connection versus partial connection), and opening in the infill plate (solid wall versus coupled wall). Regardless of the infill plate design, the steel plate wall specimens exhibited excellent strength, deformation capacity, and energy dissipation capacity, although the walls with bolt-connected infill plates exhibited a slightly lower deformation capacity. This result indicates that for architectural reasons and enhancement of constructability, various infill plate designs can be used in practice without a significant reduction in the structural capacity of the steel plate walls. The strength and energy dissipation capacity of the steel plate wall specimens with various infill plate designs were predicted by proposed methods. The prediction results were compared with the test results.

The design of slotted end hollow structural section connections in tension, according to the philosophy behind contemporary specifications [ANSI/AISC 360-05, CAN/CSA-S16-01, and EN 1993-1-8; 2005 (E)], requires checking several limit states to determine the connection capacity. From published data for these types of connections by the writers and other international researchers, a review and analysis of all prior work in this field has been made, with a focus on the current AISC specification. As a result, a new procedure for determining the capacity of such connections in tension is presented, which is shown to be a significant improvement over current international design provisions. Moreover, it is also shown to be applicable to elliptical, square, and rectangular hollow sections.

This paper presents a series of tests on high strength aluminum square hollow sections subjected to concentrated bearing load. A total of 64 web-bearing tests was conducted. The test specimens were fabricated by extrusion using 6061-T6 heat-treated aluminum alloy. The tests were carried out under end and interior loading conditions, where the specimens were seated on a fixed solid steel base plate. These tests closely simulated the support condition of the floor joist members seated on solid foundation. The test results were compared with the design strengths obtained using the American Aluminum Design Manual and European code for aluminum structures. It was shown that the design strengths predicted by these codes are either quite conservative or unconservative. Furthermore, the Australian Standard AS4100 and British Standard BS5950 Part 1 were used for aluminum square hollow section with sharp corners. The design rules of steel codes were modified to predict the web-bearing strength based on this study. It was shown that the design strengths calculated using the modified web-bearing design rules are generally conservative and agree well with the experimental results. Furthermore, the critical values of web slenderness were proposed beyond which web buckling governs.

This paper investigates the action of an individual bouncing on a structure, including the load generated and the effect on the dynamic behavior of the structure. A simply supported beam at The University of Manchester is used as a supporting structure for an individual bouncing and its responses to bouncing are recorded. Four hundred thirty three tests were conducted ranging bouncing frequency from $0.4\text{to}3.2\mathrm{Hz}$ for determining the load factors of individual bouncing loads. Over 7,300 bouncing frequencies are identified from the tests and analyzed statistically for examining how well people respond to metronome or music beats. The frequency range for coordinated bouncing between individuals is determined and is between 1.0 and $3.1\mathrm{Hz}$ . The first four dynamic load factors or Fourier coefficients are determined based on the measurements and the concept that dynamic responses induced by the sum of harmonic functions are at discrete loading frequencies. The proposed load model is validated by comparing the predicted responses and measurements on another beam. Two hundred forty human-structure interaction tests for an individual bouncing are also conducted. It reveals that a bouncing person interacts with the test rig, but the degree of the human-structure interaction is less significant than that between a standing person and the rig.

Square lighting poles with sharp or round corners have been observed to exhibit large amplitude oscillations with a frequency that is near that of their first mode. This frequency is one order of magnitude lower than that of the vortex shedding frequency for the observed wind speeds. As such, lock-in resonance between the vortex shedding and the poles motions has been ruled out as the cause of these oscillations. In this work, numerical simulations of flows over square cylinders with different aspect ratios and cross-sectional shapes have been carried out to explore and quantify low-frequency variations of the aerodynamic forces and their sources. The results show that low-frequency components are a basic aspect of the flow over finite length cylinders and are associated with the three-dimensional flow characteristics near the free end of the cylinder. This aspect is related to the loss of synchronization of the vortex shedding which, in turn, results in variations of the mean drag coefficient along the cylinder. This ability to numerically simulate the flow over a lighting pole and detailed results, as presented here, could be used to overcome wind tunnel test limitations imposed by the size of the test section and blockage ratio, and of meeting geometric similarity requirements for high aspect ratio configurations. Consequently, results from such simulations could play an important role in improving code specifications which, to date, have been based on wind tunnel simulations.

Recent earthquakes have shown that research in earthquake engineering has to be focused on the assessment of vulnerability of existing constructions lacking appropriate seismic resisting characteristics. In fact, older buildings, designed and constructed until the late 1980s, without considering earthquake provisions, constitute a significant hazard in many cities of southern Europe. Therefore, the retrofit should be made in order to reduce the vulnerability, and, as a consequence, the risk to currently accepted levels. To this scope, the scientific community is developing more accurate methodologies in order to evaluate seismic performances of existing structures. Within this framework, the present paper aims at the evaluation of the mean annual frequency of exceeding a limit state of existing concrete frames by means of the probabilistic approach introduced by the Pacific Earthquake Engineering Research, adopting the application procedure suggested by Jalayer and Cornell and accounting for the uncertainties involved in the seismic response of structures. This procedure properly combines the probabilistic seismic hazard analysis with probabilistic seismic demand analysis and, finally, with the probabilistic seismic capacity analysis. In order to evaluate the seismic reliability of existing structures taking also into account for the model uncertainty, in this paper reference is made to experimental results derived from technical literature. In particular, three full-scale frames (bare frame, frame with brick infilled walls and frame with infilled walls reinforced with shotcrete) tested pseudodynamically at the ELSA Laboratory of Ispra have been considered. The developed analysis allowed to evaluate the seismic reliability of the bare frame, the influence of the infill panels, and, finally, the reliability of the retrofitting solution with shotcrete.

This paper addresses the integrated design of civil engineering structures with control systems. Simultaneous optimization of such controlled structures is considered, showing that new alternative solutions can be achieved through integrated design. A procedure for design of controlled structural systems is developed using a two-stage approach: (1) a design of an optimal control system using a linear quadratic regulator algorithm; and (2) a redesign using an optimization procedure to match the performance of the controlled system obtained in (1). A linear single degree of freedom steel portal frame and a linear nine degree of freedom shear-type structure are used as examples to illustrate the feasibility of the proposed approach that reduces the structural weight of buildings by incorporating active or passive control elements while preserving the performance objectives.

A spatially dense wireless sensor network was designed, developed and installed on a long-span suspension bridge for a $3\text{-}\text{month}$ deployment to record ambient acceleration. A total 174 sets of data $\left(1.3\mathrm{GB}\right)$ were collected from 64 sensor nodes on the main span and south tower of the Golden Gate Bridge. Analysis of the vibration data using power spectral densities and peak picking provide approximate estimates of vibration modes with minimal computation. For more detailed analysis of the data, autoregressive with moving average models (ARMA) give parametric estimates of vibration modes for frequencies up to $5\mathrm{Hz}$ . Statistical analysis of the multiple realizations give the distributions of the vibration frequencies, damping ratios, and mode shapes and 95% confidence intervals. The statistical results are compared with vibration properties using the peak picking method and previous studies of the bridge using measured data and a finite-element model. Analysis of the ambient vibration data and system identification results demonstrate that high spatial and temporal sensing using the wireless sensor network give a high resolution and confidence in the identified vibration modes. The estimation errors for the identified vibration properties are generally low, with frequencies being the most accurate and damping ratios the least accurate.

This technical note presents a convenient modeling/design procedure for a class horizontal setback building to minimize the adverse effect of in-plane floor flexibility. Existence of such a class requires proportional eigenvalue problems of all the constituting frames regardless of the floor properties. For L, T, + etc. shape of buildings, the eigenvalue problem (of the frames) along two orthogonal directions need not be proportional. Moreover, the presence of a nonrectangular joint region theoretically precludes the existence of such a class. A step-by-step proportioning procedure, in the presence of a nonrectangular joint region, is outlined such that (1) “nearly” rigid floor modes exist, and (2) participation of the flexible floor modes under spatially uniform ground motion is close to zero.