International Journal of Civil Engineering
Volume:16 Issue: 6, Jun 2018

The purpose of this study was to determine the effect of steel/polypropylene hybrid fibers on the mechanical properties and microstructure of ultra-high-performance concrete (UHPC). Tests were carried out on UHPC without and with fibers (steel and/or polypropylene in amounts of 0.25–1%). In this study, granite or granodiorite coarse aggregate with a grain size of about 2/8 mm was employed. The three-point bending tests displayed prolonged post-peak softening behavior. In addition, increasing the content of polypropylene fibers reduced the fracture energy. Moreover, the SEM results illustrated that adding a certain amount of fibers to concrete considerably changes the microstructure. It was observed that the smallest micro-cracks in the interfacial transition zone between the paste and aggregate occurred in the concrete containing steel fibers.

This study describes the work carried out with the intention of accomplishing the ultimate objective of effective damage detection in structures, using their vibration parameters. As compared to the other vibration parameters, i.e., mode shape curvatures, damage indices, and flexibility curvatures, modal strain energy method (MSEM) showed high stability of damage detection. However, MSEM requires the information of a baseline model or healthy structure, which is then compared with that of a tested structure, to locate any stiffness reduction. In this paper, a baseline-free approach is presented to improve the accuracy of damage detection using the MSEM. Results from numerical simulations with experimental testing on a beam are presented by considering various damage scenarios, i.e., single and multiple damage with damage severity as small as 25% and as large as 50% thickness reduction. For all cases, the proposed approach is found to generate results with comparatively fewer noisy peaks in the damage index without requiring any reference or baseline data.

River confluences have complex hydrodynamics than ambient flows due to different flow characteristics of the two merging flows. Secondary circulation develops due to merging of two flows which leads to bed erosion. The eroded sediment gets deposited at various locations in the downstream of the confluence. It is reported in the literature that major reservoirs in India will lose 50% storage capacity by 2020 and reservoirs all over the world lose storage capacity by as much as 5% every year. In view of controlling bed erosion at the confluence, vane and circular pile models are used as scour mitigation structures and experimental results are presented. Experiments are performed in a distorted model with a non-uniform sediment of mean particle size d 50  = 0.28 mm with a confluence angle of 60°. Two different discharge ratios (Qr = ratio of lateral flow discharge to main flow discharge) of 0.5 and 0.75 are used with a constant flow depth (Hm) of 5 cm in the main channel. Vanes of width 0.3Hm (1.5 cm), thickness of 1 mm are placed at 15°, 30° and 60° vane angles with respect to main flow. Circular pile models of 8 and 12 mm diameter are also used. Two different spacing of 2Hm and 3Hm (10 and 15 cm) between the vanes or piles are used to perform the experiments. For Qr = 0.5 and 0.75 using vanes, scour depth reduces by 25 and 34%, respectively. When circular pile models of 8 and 12 mm are used, the scour depth reduces by 25, 38 and 27, 43%, for Qr = 0.5 and 0.75, respectively. The scour depth decreases with an increase of vane angle and pile diameter, but increases with an increase of spacing. Therefore, piles have better performance over vanes in reducing scour at the confluence.

In scope of the study, behavior of timber-framed shear walls having openings with variable dimensions and locations subjected to reverse cyclic loading is experimentally investigated. Main variables considered in the study are the aspect ratios of timber-framed panel walls, dimensions and locations of the openings on the panel walls, material of the timber frames and spacings of the nails used in the panel connections. Load–displacement relationships, strengths, stiffnesses, displacement ductility ratios, energy dissipation capacities and failure mechanisms of the specimens are determined. The ultimate load capacities of the timber-framed panels are calculated as per Eurocode 5 and presented in comparison to experimental results. Moreover, lateral load-resisting capacities and load–displacement relationships of the test specimens are numerically calculated with finite element analyses. A good agreement was observed between the numerical and experimental results. From the test results, it is observed that the load behavior relationships of the test specimens significantly affected by aspect ratios, location of the openings, material of the timber frames and spacing of the nails used to provide connection between the timber-framed panel elements. Also, the increasing size of the openings decreased the stiffness’ of the test specimens.

Emerging GPS devices enable new data collection opportunities for transit performance monitoring. In addition to the fact that GPS devices can replace labor-intensive survey techniques, they also collect traffic information throughout transit routes that the traditional fixed loop detectors cannot. If public transit vehicles are equipped with GPS devices, it is possible to monitor the performance of public transit services throughout the routes and alert the associated authorities at significantly lower costs about potential problems for corrective actions to be taken. Transantiago, a major public transit service provider in Santiago, Chile, has recently installed GPS sensors on all its vehicles which provides an excellent venue on which an innovative transit monitoring methodology can be modeled and applied. This paper first conducts current-status analysis on distributions of headways throughout a route in Santiago by processing extensive raw GPS data from transit vehicles. Then, unique transit headway adherence indices are developed with respect to the expected passenger waiting time and are presented in forms of two-dimensional tempo-spatial graphs. The analysis of real-life data collected from bus GPS probes in Santiago, Chile indicates that GPS devices in transit buses can effectively provide the proposed performance measures throughout the route on a daily basis.

One of the methods to improve adhesion between asphalt binder and aggregate and to reduce moisture susceptibility in asphalt mixtures is aggregate treatment using suitable coats which cause to change aggregate polarity. In this study, effect of nanomaterial coating on aggregate over moisture damage of HMA by means of thermodynamic and mechanical methods has been probed. Aggregates used in this study are granite and limestone that have been modified using iron oxide and aluminum oxide nanoparticles. Results illustrate that in comparing modified samples through nanoparticles with control samples, tensile strength ratio on moisture condition surpasses dry condition. Surface free energy result shows that aggregate coat with nanoparticles leads to decrease in differences between free energy of adhesion in moisture condition and dry condition, and thus, stripping event is diminished. Nanoparticles’ positive performance of iron oxide compared with aluminum oxide nanoparticles in decreasing the moisture sensitivity of asphalt mixtures built is more evident about either kind of aggregates.

This study introduces a mathematical model to represent the hysteresis behavior of structural systems. Compared with some of the analytical models currently in use, this model (which considers different structural phenomena, including pinching, stiffness degradation, strength deterioration, and sliding) yields more precise responses. This model is based on Mostaghel’s well-known model, although some essential modifications and sliding effects are also considered. The model is developed based on a simple single-degree-of-freedom multi-linear mechanical system and on the development of partial differential equations. The proposed model includes the basic characteristics of the hysteresis cycles that can be easily measured through experimental tests. To demonstrate the degrading phenomena of the hysteresis behavior of the structures, several examples of different actual structural systems are presented, to show that the proposed analytical model can provide realistic descriptions of the structural hysteretic performances. In addition, comparisons between the outputs of this model and some hysteretic curves of other models are presented to show the high capability and accuracy of the proposed model.

Chloride-induced corrosion continues to the main cause of deterioration of concrete structures in the marine areas. To introduce the high rate of corrosion in Persian Gulf area, the axial load-carrying capacity of reinforced concrete columns, which have been exposed to the real corrosive condition of this area about 1.5 years, is measured. Then, a new framework for long-term seismic evaluation of existing corroded reinforced concrete bridge in this area is proposed. Calculation of corrosion initiation time, development of material model considering effects of corrosion, moment–curvature analysis of bridge columns, determination of plastic hinge characteristics, and pushover analysis in longitudinal and transverse directions of the bridge are the main steps of proposed framework. Effects of corrosion include the degradation of cover and core concrete, steel bar, and bonding between concrete and steel bar. By comparing the obtained seismic capacity of bridge at specific time points in bridge service life, effect of corrosion on the long-term seismic performance of bridge is determined. On the basis of analysis results, due to ensuring the long-term seismic performance of seismically designed reinforced concrete bridge in the marine area after 90 years of service, it is suggested in this paper that the design base shear should be increased by 12.5%.

Based on the limitations of traditional procurement, this study uses analytical network process (ANP) for contractor selection. Using extensive literature review, best value (BV) contributing factors are identified. Experts are involved to get their feedback for shortlisting the identified factors. An ANP-based decision support system has been developed using data collected through a detailed questionnaire survey in the local construction industry for evaluating the selection process. Further, five case studies of completed road construction projects have been used to validate the decision support system. The findings indicate that in almost all the cases, the traditional procurement system, owing to its stringent prequalification measures, subliminally took into consideration the overall value proposition, and only one case study showed anomalies for which detailed reasoning is deliberated. This highlights the tendency of practitioners to overweigh the cost-based criteria, despite an established significance of other factors, treating the intangible value factors of quality, health and safety, environmental impact, etc. as less important. It reflects that the local construction industry attaches marginal value to qualitative factors. The construction industry will benefit from implementation of BV procurement system and a prolonged exposure may help improve its value system to realize the contribution of non-cost-based factors.

In this study, cost-effective polyester fiber reinforced polymer (PFRP) composite plates were used as external strengthening materials of conventional reinforced concrete (RC) beams. The flexural behavior of PFRP strengthened RC beams was investigated. Two RC control beams and six PFRP strengthened RC beams were constructed and tested under four-point bending. The dimension of these concrete beams used was 150 mm × 300 mm × 2000 mm. The experimental variables included thickness of PFRP (four and six layers of laminates) plates and steel reinforcement ratio (0.223 and 0.503%). The test results indicated that compared with the control beams, the strengthened beams experienced significant enhancement in ductility, ultimate load and deflection due to the PFRP reinforcement. The increase in transverse load due to PFRP strengthening was more pronounced for the RC beam with a low steel reinforcement ratio (0.223%). The ductility (calculated from both displacement-based and energy-based approach) of the PFRP strengthened RC beam with the low steel ratio was larger than that of the strengthened beams with the large steel ratio. The experimental ultimate loads of the PFRP strengthened beams were also compared with the predictions based on the equation given in ACI 440.2R-08 proposed for RC beams strengthened by synthetic glass or carbon FRP materials. This study, therefore, implied that the PFRP has potential as external strengthening materials of concrete structures.