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Concrete beams reinforced with rectangular spiral shear reinforcement instead of the ordinarily closed stirrups have been recently extended. However, this extension has never been addressed for light-weight concrete structural elements. An experimental program is conducted in this research to investigate the shear performance of light-weight concrete beams that are transversely reinforced with continuous rectangular spirals. Four groups, including 20 specimens, were constructed where the groups contain two different shear span to depth ratios of 2.0 and 1.5 and have two different spiral spacing of 200 mm and 150 mm. Five different inclination angles of the spiral reinforcement were considered for each group: 85°, 80°, 77.2°, 75o, and 72.5°. The beams were tested under static four-point loading. Test results have shown that using rectangular spiral reinforcement has enhanced the shear capacity and deflection of the test specimens. Shear strength enhancement has ranged from 3% up to 47% compared to the ordinarily closed stirrups. Test results have also shown that the angle of inclination, which would result in the best performance, is influenced by the shear span to depth ratio. The optimum angles were found 85° and 75°, for the shear span to depth ratio of 2.0 and 1.5, respectively.

The torsional behaviour of high-strength concrete beams that are transversely reinforced with continuous spiral reinforcement is experimentally investigated in this research. Seventeen specimens ar...

PurposeThe main goal is to investigate the effect of size and location of opening and column size on the punching shear strength. Openings are often needed in order to install mechanical and electrical services. This process takes away part of the concrete volume which is responsible for resisting the shear forces and any unbalanced moment. Furthermore, the application of rectangular columns in flat slabs is commonly used in practice as they provide lateral stiffness to the building. They are also utilised in garages and multi-storey buildings where these elongated cross-sectional columns reduce the effective span length between adjacent columns.Design/methodology/approachThis research is a numerical-based investigation that is calibrated based on a thirteen previously tested and numerically calibrated slab specimens with no openings. A parametric study is conducted in this study to consider the effect of other parameters, which are the size and location of opening and the rectangularity ratio of column in order to evaluate their effect on the punching shear capacity. A total of 156 models are developed to study these factors. Additionally, the predicted shear carrying capacity of the simulated slabs is calculated using the ACI318–19 and Eurocode (EC2-04) equation.FindingsThe presence of openings reduced the punching shear capacity. The small opening's location and orientation have almost no effect except for one slab. For slabs of large openings, the presence of openings reduced the punching capacity. The punching capacity is higher when the openings are farther from the column. The numerically obtained results of slabs with rectangular columns show lower punching capacity compared to slabs of squared columns with the same length of the punching shear control perimeter. The punching capacity for all slabs is predicted by ACI318–19 and Eurocode (EC2-04) and it is found that Eurocode (EC2-04) provided a closer estimation.Originality/valueThe slabs considered for calibration were reinforced with four different punching shear reinforcement configurations, namely; ordinary closed rectangular stirrups, rectangular spiral stirrups, advanced rectangular spiral stirrups and circular spiral. Generally, there has been limited research on concrete flat slabs with openings in comparison with other subjects related to structural engineering (Guan, 2009) and no research on punching shear with openings of slabs reinforced with these reinforcement schemes. The available research focussed on the effects of openings on the flexural behaviour of reinforced concrete slabs includes Casadei et al. (2003), Banu et al. (2012) and Elsayed et al. (2009). In addition, experimental tests that examined slabs supported on rectangular columns are very limited.

Replacing traditional closed stirrups by rectangular spiral reinforcements in concrete beams constructed using self compacting concrete (SCC) is experimentally investigated in this paper by testing twenty beams under static loading. The shear performance of SCC beams is evaluated by measuring the maximum shear load values, load-deflection curves, and crack propagation for all tested beams. Two different spirals spacing of 200 and 150 mm and five different angles of inclination for the spiral reinforcement (85°, 80°, 77.2°, 75°, and 72.5°) are adopted. The experimental shear capacity results are compared with theoretical shear strength determined by the (ACI 318) code. The results indicated that using of continuous spiral reinforcement improves the shear capacity of SCC beams up to 16.67% increase in comparison to traditional closed stirrups. Moreover, the results showed that optimum performance depends on the angles of inclination, where 85° was the optimum angle of inclination regardless of pitch spacing. It is recommended to use the continuous spiral reinforcements in SCC beams because it enhances the shear capacity, and reduces time and labor cost needed in construction.

Purpose The purpose of this paper is to detect damages in steel structures with actual connections, i.e. semi-rigid connections. The method will detect the damages by tracking the changes in the stiffness of structural members using only a limited number of dynamic responses and without knowing the type or time history of the dynamic force applied on the structure. Design/methodology/approach The paper proposes a technique that combines the iterative least-square and unscented Kalman filter (UKF) methods to identify the stiffness of beams and columns in typical two-dimensional steel-framed structures with semi-rigid connections. The detection of damages is by using nonlinear time-domain structural health monitoring method. Findings The technique is verified by using numerical examples using noise-free and noise-included dynamic responses from two different types of dynamic forces: harmonic and blast loads. The results showed that the UKF method with iterative least-square is a powerful approach to identify and detect damages in structures that have nonlinear behavior and the method was able to detect the damages in beams with a very high accuracy for noise-free and noise-included dynamic responses. In addition, the optimum number and locations of dynamic responses (accelerometer sensors) required for damage detection were determined. Originality/value This paper fulfills an identified need to detect damages in steel structures using only a limited number of accelerometer sensors.

Traditional designs of sleeve couplers for tube and fitting scaffolds only require the maximum moment capacity of the coupler under pure bending configurations. The normal design assumptions are that the stiffness of the coupler does not vary under different axial loads. Looseness and the axial load transmitted through the tube on to the coupler are not considered to have any effect. Tests have been undertaken to investigate the looseness occurring within the connection and the influence of side loads, such as those that occur under wind or eccentric loading, on the stiffness and maximum moment capacity of the couplers. The tests showed that the looseness is negligible (less than 0.002 rad) under tests consisting of four-point bending with no axial loads. However, when tests with axial loads held static at 25, 50 and 75% of the maximum axial load that the coupler can carry; and with side loads cycled three times with side loads of up to 5 kN applied to the coupler; that the connections exhibited loosenesses of up to 0.037 rad and the maximum moment capacities reduced by up to 47% of a coupler without side loads. This paper therefore recommends that design codes be altered to insist on the influence of side loads on coupler performance being taken into consideration to ensure safe structures.

The use of continuous rectangular spiral shear reinforcement as transverse reinforcement is experimentally investigated by testing 28 reinforced concrete beams in a static four-point bending setup. In this paper two shear span-to-depth ratios (2.5 and 3.0), three spacing (125, 150 and 200 mm) and five inclination angle of stirrups (62, 70, 75, 80 and 85°) are adopted. The behavior of the shear-critical beams is studied through monitoring the load–deflection curves, ultimate load values, vertical deflections measurements and crack propagation during static tests. The experimental shear capacity of the beams are compared with analytical values from the design shear formulas of ACI 318M-14 code. Test results clearly indicate that using rectangular spiral shear reinforcement improved the shear capacity and ductility of beams compared with traditional individual closed stirrup beams. Furthermore the results showed that the optimum inclination angle for spiral stirrups is 80°. Accordingly, using rectangular spiral shear reinforcement is recommended because it improves the shear capacity and ductility in beams and can reduce the total cost due to labor costs.

The standard design procedure for tube and fitting connections assumes that the connections are only subjected to non-cyclical loads. This paper presents the results of experimental tests and theoretical calculations of the moment-rotation capacities of three common connections – sleeve couplers, swivel couplers and right-angled couplers. The results show that under a cyclic side load, such as that occurring by wind loading, looseness affects the capacity of the connections. For all three types of coupler looseness is shown to be relatively high which will reduce the stiffness of the connection under side loads. For sleeve couplers the effects of axial load in the tubes also affects the coupler stiffness and the maximum bending capacity of the joint. This implies that the common European code BS EN 74–1 for the connection should be changed to consider the loss in stiffness and maximum side load capacity under axial loads and looseness which are ignored in the standard. The standard assumption for right-angled and swivel couplers is that the connection can be assumed to be rigid about an axis normal to the plane containing the two tubes being joined. This is shown to be incorrect as the connections are shown to have stiffnesses about this axis which is of a similar order to the stiffnesses about the other axes.

Pushover analysis is becoming recently the most practical tool for nonlinear analysis of regular and irregular highway bridges. The nonlinear behaviour of structural elements in this type of analysis can be modeled through automated-hinge or user-defined hinge models. The nonlinear properties of the user-defined hinge model for existing highway bridges can be determined in accordance with the recommendations of the Seismic Retrofit Manual by the Federal Highway Administration (FHWA-SRM). Finite element software such as the software SAP2000 offers a simpler and easier approach to determine the nonlinear hinge properties through the automated-hinge model which are determined automatically from the member material and cross section properties. However, the uncertainties in using the automated-hinge model in place of user-defined hinge model have never been addressed, especially for existing and widened bridges. In response to this need, pushover analysis was carried out for four old highway bridges, of which two were widened using the same superstructure but with more attention to seismic detailing requirements. The results of the analyses showed noticeable differences in the capacity curves obtained utilizing the user-defined and automated-hinge models. The study recommends that bridge design manuals clearly ask bridge designers to evaluate the deformation capacities of existing bridges and widened bridges using user-defined hinge model that is determined in accordance with the provisions of the FHWA-SRM.

A novcl system identification and structural hcalth assessment proccdurc of steel finn~ed structures with semi-rigid connectiol~s is prescntecl in tliis paper. It is capable of ilctecting damages at the local elc~ncr~t level under nonnal operating conditions; i.e., serviceability limit state. The procedure is a linear time-domain system identification tecllnique in which the structure responses arc required, whereas the dynamic excitation force is not recluircd to identifjl thc strtlctural parameters. The procedure hacks changcs in the stiffiiess properties of all the elements in a stnlcture. It can identify damage-frec ancl (lamaged stnictural elemenls vely accurately whcn excited by different types of' dy~ramie loadings. 'l'he method is elaborated witli the llclp of' several numerical examples. Tlle results indicate that the proposed i~lgoritll~n identified tlle structures correctly and detected the prc-imposed danlages in the frames when excited hy earthquake, impact, and harmonic loadings. '1:Ile algorithm can potentially be used for structural llealtli asse,ss~rie~~t and monitoring of existing shxctures witli lninimum clisnlption of operations. Since the procedure requires only a few time points of response infotmation, it is cxpccted to be economic and efficient.

The large-deflection spring behavior of an inextensible thin rhombus frame is studied in this work. The frame has a rectangular cross-section and supports two equal and opposite diagonal forces that act on its two opposite corners with a given apex angle γ. Both geometrical and material nonlinearities have been considered in the study. The beam was assumed to be made of a material having a nonlinear stress–strain relationship of the Ludwick type. A semi-analytical solution has been formulated for the relation between the large displacement at the corners of the frame and the applied forces. The deformed shapes and the nonlinear secant stiffnesses of the rhombus frame were plotted against applied loads. The frame behavior was fully investigated for different apex angles and nonlinear elastic material constants, n. In order to check the accuracy and efficiency of the proposed analytical solution, a large-displacement finite-element analysis utilizing the multi-purpose computer program ADINA was performed. Each side of the rhombus frame was divided into 10 moment–curvature beam elements. Results obtained using the analytical solution were identical to the results obtained using the software ADINA.

A new technique was proposed for the large deflection problem of a prismatic composite cantilever beam made of two different nonlinear elastic materials and subjected to an inclined tip concentrated force. Two types of composite cantilever beams were considered in this study: A solid rectangular and a hollow circular cross-section beam. The proposed technique assumes that the behavior of a composite cantilever beam is equivalent to the behavior of two homogeneous cantilever beams. A semi-analytical solution describing the complete behavior of each homogeneous beam was derived and the complete deflection curve of the composite cantilever beam was obtained by considering the weighted average deflection curves of the two homogeneous cantilevers with respect to the tip forces. Several numerical examples were presented at the end of the study. Results obtained using the proposed technique were compared with results obtained using the software ADINA and found to be in good agreement.

A two-stage finite element system identification (SI) technique is proposed in this paper to identify stiffness of elements and detect damages in three-dimensional framed structures. The technique combines in stage 1 the iterative least-square and in stage 2 the unscented Kalman filter (UKF) to identify the stiffness of elements using only limited measured response time histories from only four to six accelerometers instead of dozens of accelerometers of the whole structure and assuming the time history of dynamic load applied on structure is unknown. The method will identify the stiffness and detect the damages in the elements by tracking the changes in the recordable dynamic output responses between damaged and undamaged states. The optimum number and locations of accelerometers were studied in this paper. The algorithm is verified using numerical examples. The results showed clearly that the technique can identify damaged and undamaged three-dimensional steel framed structures and the minimum number of sensors required for such frames.