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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.

The axial compressive behavior of fifteen reinforced concrete columns that were constructed from four types of aggregates: Natural Aggregate (NA), Recycled Asphalt Pavement (RAP), Recycled Coarse Aggregate (RCA), and RAP-RCA were studied experimentally and theoretically. The NA was replaced by RAP and RCA at five replacement levels: 20%, 40%, 60%, 80% and 100% by the total weight of NA. In addition of combining RAP and RCA in the same mixes with replacement levels of: 20% RAP-80% RCA; 40% RAP-60% RCA; 60% RAP-40% RCA; and 80% RAP-20% RCA. The axial compressive behavior of the columns was studied through reporting the ultimate load values and the crack propagation during static tests. The experimental axial capacity of the columns was compared with the theoretical values determined by ACI and Japanese codes. The experimental results showed that there was a reduction in the axial capacity of columns when the RAP, RCA, and RAP-RCA contents increased. However the calculated theoretical values were more conservative comparing to the experimental values. This provides a very positive indication that the RAP, RCA, and RAP-RCA columns can be used in the structures safely and the RAP-RCA combination is a promising technique.

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.

Atomistically informed multiscale dislocation dynamics plasticity (MDDP) framework is used to investigate the mechanical response and microstructure evolution in bulk magnesium single crystals subjected to c-axis compression. The MDDP framework was modified to account for the 〈c + a〉 dislocation slip on the pyramidal I and pyramidal II planes. Several aspects of the 〈c + a〉 dislocation reactions such as the transition of pyramidal I near edge and pyramidal II pure edge segments to basal plane, and the thermally activated cross slip are considered. Additionally, a generalized mobility law and anisotropic frictional stress models are implemented based on the findings of several molecular dynamics studies. MDDP predictions of the yielding and strain hardening behaviors, as well as the maximum stress prior to failure are in good agreement with the reported experimental values. Moreover, detailed study of the dislocation microstructure evolution and the dislocation density dependence on the applied stress are presented and compared with available experimental results.

This paper presents the results of a study that investigated the improvement of the mechanical properties of recycled concrete aggregate (RCA) produced by adding chopped basalt fibers (BF) with contents of 0.1%, 0.3%, 0.5%, 1%, and 1.5% by total volume of the mix to treated and untreated recycled aggregates. The recycled aggregates were surface treated by pre-soaking them in a 0.1 M hydrochloric acid (HCl) solution for 24 h to remove the adhered mortars to improve the bond between the recycled aggregate and the cement. In addition, chopped BF was added to normal concrete (NA) mixes as a control for comparison. The results showed that using chopped BF minimally enhanced the compressive strength of the concrete mix but significantly improved its flexural and splitting tensile strength. Furthermore, the optimum BF content that produced the same splitting tensile and compressive strength as NA was 0.5% for untreated RCA and 0.3% for treated RCA, while the flexural strength was 0.3% for untreated RCA and 0.1% for treated RCA.

This paper presents the results of a study that investigated the improvement of the mechanical properties of coarse and fine recycled asphalt pavement (RAP) produced by adding silica fume (SF) with contents of 5%, 10%, and 15% by total weight of the cement. The coarse and fine natural aggregate (NA) were replaced by RAP with replacement ratio of 20%, 40% and 60% by the total weight of NA. In addition, SF was added to NA concrete mixes as a control for comparison. Twenty eight mixes were produced and tested for compressive, splitting tensile and flexural strength at the age of 28 days. The results show that the mechanical properties decrease with as the content of RAP increases. And the decrease in the compressive strength was more in the fine RAP mixes compared to the coarse RAP mixes, while the decrease in the splitting tensile and flexural strength was almost the same in both mixes. Furthermore, using SF enhances the mechanical properties of RAP mixes where the optimum content of SF was found to be 10%, and the mechanical properties enhancement of coarse RAP were better than fine RAP mixes. Accordingly, the RAP has the potential to be used in the concrete pavements or in other low strength construction applications in order to reduce the negative impact of RAP on the environment and human health.

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.

This paper investigates experimentally and theoretically the shear behavior of thirteen reinforced concrete (RC) beams made of Recycled Asphalt Pavement (RAP) and Recycled Coarse Aggregate (RCA). The span length of the beams was 2240 mm, and the width and depth of the beams were 200 and 400 mm, respectively. Three groups of beams were used in this study: The first group was five beams made of RAP and natural aggregate (NA), where the NA was substituted by RAP with replacement levels of 20%, 40%, 60%, 80%, and 100% by the total weight of NA. The second group was four beams made entirely of RAP and RCA. The third group was four RC beams made of RCA and NA, where NA was replaced by RCA with replacement levels of 20%, 40%, 60%, and 80%. The beams were tested under four-point loading setup. The maximum shear forces, deflections, and cracking patterns were studied. The experimental results were compared with theoretical results determined from the equations of selected international codes and fracture mechanics approaches available in the literature. The results showed that the experimental shear capacity increased as the RAP and RCA replacement levels decreased for the beams in group one and three, and decreased for group two beams when the RCA replacement levels increased. The theoretical shear strength capacities were more conservative when compared to the experimental results. Therefore, the theoretical shear equations can be applicable to the beams constructed with recycled aggregates. In general, using RAP and RCA in RC beams can be considered as an effective approach.

The effect of fire on reinforced concrete (RC) structures is very important because it is threatening the human life and property safety. Using Recycled Asphalt Pavement (RAP) and Recycled Coarse Aggregate (RCA) in concrete mixtures can be considered economically and environmentally friendly because it saves our natural resources. This paper investigates experimentally the influence of incorporating RAP and RCA on the mechanical properties of concrete mixes after exposure to different temperatures: 20 °C, 200 °C, 400 °C, and 500 °C. The Natural Coarse Aggregate (NCA) was replaced by RAP aggregates at three replacement ratios (10%, 20% and 30%), and the NCA was replaced by RCA at four replacement ratios (20%, 40%, 60%, and 100%). As well as using three mixes of 90%RCA-10%RAP, 80%RCA-20%RAP, and 70%RCA-30%RAP. Compressive, splitting tensile and flexural strengths, compressive stress-strain curves, and modulus of elasticity were studied on two hundred sixty four cylinders and one hundred thirty two prisms. The results showed that the mechanical properties decreased as the replacement ratios of RAP and RCA increased for the same temperature. And the mechanical properties decreased for the same replacement ratio of recycled aggregates when the temperature increased. The decrease in mechanical properties at elevated temperatures for RAP-RCA mixes can be comparable with NCA, RAP and RCA only mixes. Therefore, the RAP and RCA have the potential to be incorporated in the concrete mixes on high temperatures since the decrease in the mechanical properties is not that significant relative to the efforts in reduction the negative impacts of recycled aggregates on the environment and human health.

The shear behavior of ten full scale reinforced concrete beams that were constructed from natural aggregate, recycled aggregate and treated recycled aggregate was experimentally and analytically studied. All beams were constructed without stirrups and with 50% and 100% recycled aggregate. The beams were tested for a shear span-to-depth ratio (a/d) equal to 2.0 and 3.0. The performance of recycled aggregate was improved through enhancement treatment methods. The recycled aggregate was pre-soaked in hydrochloric acid (HCl) for 24 h to remove adhered mortars attached to original recycled aggregates, and then they were impregnated with sodium metasilicate pentahydrate solution for one hour to coat their surfaces. The behavior of the shear-critical beams was studied through reporting the load-deflection curves, ultimate load values, and crack propagation during static tests. The experimental shear capacities of the beams were compared with theoretical values from different international codes and fracture mechanics approaches. The experimental results showed that in general using treated recycled aggregate improved slightly the shear capacity of the beams in comparison with natural and untreated recycled aggregate. Furthermore, the shear strength comparisons showed that the treated recycled aggregate beams were considered more conservative compared to the natural and untreated recycled aggregate beams regardless of the shear span-to-depth ratio.

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.

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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 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.

The nonlinear free vibration and frequency veering of a single wall carbon nanotube (SWCNT) based on nonlocal elasticity theory is studied and investigated in this paper. The carbon nanotubes (CNT) is assumed to have an imperfection modeled as half sine and clamped at both ends. The Euler-Bernoulli Beam and Hamilton’s principle were used to derive the nonlinear equation of motion of the SWCNT. The effect of; nonlocal elasticity, geometric initial rise/imperfection, and the effect of the axial force induced by mid-plane stretching are accounted for in the derivation of the nonlinear mathematical model of the CNT. The governing partial differential equation includes quadratic and cubic nonlinearities due to the initial imperfection and the mid-plane stretching. The derived equation of motion is discretized using the assumed mode method by inserting the exact linear eigen mode shape. The resulting nonlinear temporal equation was solved using the method of multiple scales (MMS) to obtain results for the nonlinear natural frequencies of the first three modes of vibrations, for different values of rise/imperfection amplitude, and for different values of the nonlocal parameter. The results are presented in non-dimensional characteristic curves to show the effect of variation of rise/imperfection amplitude and nonlocal parameter on the vibrational behavior of the CNT.