International Journal of Structural Engineering (8 papers in press)

Regular Issues

• Impact Resistance of Waste Tyre Rubber and Silica Fume based Concrete Mixes  
  by Satnam Singh, Gurpreet Kaur 
  Abstract: In this paper, the feasibility of using waste tyre rubber and silica fume based concrete mix is tested for designing non-structural applications that can bear a sudden impact of specified limit. The compressive strength and impact resistance is tested for 10 different concrete design mixes (as per Indian Standard Codes) in which coarse aggregates, fine aggregates and cement is replaced with varying proportions of chipper rubber (10%, 15%, 20%, 30%), crumbed rubber (10%, 20%, 30%) and silica fume (5%, 10%, 15%) respectively. The mechanism used for repeated-impact testing is manually designed using drop-weight method. The comparative analysis of compressive strength & impact resistive of proposed concrete mix is performed with conventional M20 grade concrete mix. It is observed that the compressive strength of waste tyre rubber and silica fume based concrete mixes is lower than the conventional (M20) concrete, while the impact resistance is higher.
  Keywords: Compressive Strength; Impact Resistance; Impact Testing; Indian Standard Codes; Rubberized Concrete; Silica Fume.
  
  
• Tensile stress limits for high strength concrete prestressed structures  
  by Fayez Moutassem, Mohammad I. Hossain 
  Abstract: High strength concrete (HSC) is regularly used in precast prestressed concrete structures. The allowable tensile stresses in various codes do not account for high early strength HSC exceeding 10,000 psi (69 MPa). In this study, design equations are developed for the tensile stress limits at the time of initial prestress and at service. An experimental program is developed and it involved the use of mineral admixtures and subjecting fresh concrete to 24 hours of accelerated heat curing to mimic actual field conditions. Comparison between various design codes (ACI 318, AASHTO, LRFD) has revealed that all the code equations significantly underestimated the allowable tensile stresses at service and are therefore too conservative. The proposed tensile stress limits would ensure a more economical design of high strength prestressed concrete members.
  Keywords: concrete; high-strength; prestressed; precast; compression; flexure; allowable stresses; heat-curing; tensile limits.
  DOI: 10.1504/IJSTRUCTE.2021.10037211
   
  
• Imperialist competitive algorithm approach to solve structural fuzzy random reliability  
  by Mohammad Haranji, Mehdi Yazdani 
  Abstract: In the presence of aleatory and epistemic uncertainties, the reliability index is a fuzzy number, instead of an ordinary (single-valued) one. A well-known approach to determine the fuzzy reliability is -cut. The fuzzy random variable is transformed into an interval random variable for each membership degree . In this method, the maximum and minimum of the reliability index corresponding to the membership degree must be obtained. The proposed fuzzy random reliability is more accurate in comparison with the classical reliability. This article applies a metaheuristic algorithm, imperialist competitive algorithm (ICA), to search the maximum and minimum of the reliability index. The obtained results using the proposed algorithm are compared with outputs of a genetic algorithm. Results show the high performance of the ICA in obtaining desirable solutions. Considering the method applied and the algorithm hybridised to obtain reliability index, this is a new issue in structural reliability.
  Keywords: imperialist competitive algorithm; ICA; structural reliability; fuzzy reliability index; fuzzy sets; uncertainty.
  DOI: 10.1504/IJSTRUCTE.2021.10037678
   
  
• Optimal residual subspace model for structural damage diagnosis: an approach independent of operational and environmental variations  
  by Kundan Kumar, Sumanshu Agarwal 
  Abstract: Several machine learning algorithms have been proposed to detect damage in civil structures that implicitly learn changes in dynamic characteristics of structures due to varying operational and environmental conditions. However, despite the intensive computational load, the methods were not able to completely mitigate the said variations. In contrast to that, here, we introduce a new methodology based on percentage of total variance (PTV) criterion for damage detection to overcome the influence of varying operational and environmental conditions on the vibration-based damage sensitive features. Using PTV criterion, an optimal residual subspace (ORS) is modelled which is applied to Mahalanobis squared distance (MSD) and singular value decomposition (SVD)-based damage detection methods. Interestingly, we find that in comparison with similar machine learning-based damage detection approaches, the proposed approach outperforms in terms of false positive reduction and overall accuracy.
  Keywords: structural health monitoring; damage detection; outlier detection; optimal residual space; percentage of total variance; PTV; eigenspace; Mahalanobis squared distance; MSD; singular value decomposition; SVD.
  DOI: 10.1504/IJSTRUCTE.2021.10038767
   
  
• Prediction of axial capacity of octagonal concrete-filled steel tube columns considering confinement effect  
  by Nazar J. Abbas, Ammar A. Ali 
  Abstract: The present research presents both detailed and simplified formulae on the octagonal concrete-filled steel tube (CFST) columns to define the ultimate strength of this type of column. These formulae have been validated and proved to be accurate through comparisons with experimental tests and with other available methods proposed by other researchers. On the other hand, employing the new formula in the constitutive model of core concrete in the finite element analsis (FEA) has shown to be of adequate accuracy to predict the behaviour of octagonal CFST columns. The effects of variation in both concrete-steel strength ratio (f'c/fy)and depth-to-thickness of the tube (D/t) (D/t) were studied. It is found that by decreasing the depth-to-thickness ratio of steel tube (D/t) the confining pressure will be increased. Also, decreasing the ratio of compressive strength of concrete to yield strength of steel (f'c/ fy)the confining pressure will be decreased.
  Keywords: axial capacity; octagonal CFST; concrete-filled tube; confinement effect; composite columns; steel tube; concrete core; finite element; constitutive model; concrete-steel strength; FE modelling; column behaviour; nonlinear FEA.
  DOI: 10.1504/IJSTRUCTE.2021.10039005
   
  
• Performance of simply supported concrete beams reinforced with high-strength polymer re-bars under blast-induced impulsive loading  
  by S.M. Anas, Mehtab Alam 
  Abstract: A finite element model is developed in ABAQUS/CAE to simulate the dynamic response of the reinforced concrete (RC) beam under close-in air-blast loading. The model is subjected to different blast pressures at different scaled distances in free air. The values of the blast pressure have been taken from the blast tests conducted on four RC beams of size 1,700 mm x 150 mm x 150 mm by the State Key Laboratory of Explosion Science and Technology (China). The finite element predictions and available test results, including maximum mid-span displacements and damage to the beams, are presented and contrasted. The validated ABAQUS/CAE model is used to investigate the behaviour of the beams with replacement of the mild steel re-bars by the polymer re-bars of equivalent tensile strength on both compression and tension sides of the beam under air-blast loading.
  Keywords: reinforced concrete; beams; air-blast; explosion; fibre-reinforced polymer; FRP; re-bars; blast pressure; displacement; CDP model; damage; cracks.
  DOI: 10.1504/IJSTRUCTE.2021.10039006
   
  
• Review of buckling restrained braces for earthquake resistant design of industrial structures in India  
  by Bhavinkumar S. Shah, Vijay R. Panchal 
  Abstract: India had already witnessed devastating earthquakes in past and may witness even higher intensity of earthquakes in the future. The industrial structures are highly irregular structures and hence they are more vulnerable to earthquakes. The earthquake resistant design related codal provisions are revised recently in India. The conventional structural systems of moment resisting frame and conventional brace are not the most efficient systems for earthquake resistant design. In this paper, buckling restrained braces (BRB) are reviewed for the industrial structures in India. In the study, heavy silo supporting structure is analysed using conventional braces and BRBs. Total six nos. of analytical models are generated and response reduction factor are evaluated using pushover analysis. BRB is not yet codified in the Indian Standards. For implementation of the system in the country, codification is required for standardisation. The more research is required to eliminate the full scale testing requirements of BRB.
  Keywords: buckling restrained braces; earthquake resistant design; industrial structures in India; seismic design; earthquake engineering; response reduction factor; retrofitting; India.
  DOI: 10.1504/IJSTRUCTE.2022.10039868
   
  
• Influence of truss-type and welded reinforcement in concrete beam  
  by H.M.A. Mahzuz, Mushtaq Ahmed, Md. Maksudul Islam, Rashadul Hasan, Kamrul Hasan, Md. Meftahul Alam 
  Abstract: In present study, the shear strength of the conventional reinforced concrete beam (here named as non-welded rectangular stirrup beam NRSB) is compared with three types of beam having modified reinforcement patterns, named as welded rectangular stirrup beam (WRSB), non-welded Warren truss beam (NWTB) and welded Warren truss beam (WWTB). Such names are given based on the stirrup orientation. All beams have the same concrete dimension and the same total weight of reinforcement, ensuring no variation of cost. From the test results, the average shear strength enhancement of WRSB, NWTB, and WWTB was found to be more than 17%, 10%, and 30% compared with conventional NRSB. WWTB was proposed to be the best alternative. To design the above-mentioned beams, design equations are proposed and verified. Use of finite elemental software reveals that in reinforcement the stress intensity (Von-mises) is the maximum in WWTB, followed by WRSB, NWTB and finally NRSB.
  Keywords: beam; coefficients; stirrup; shear strength enhancement; Warren truss; welding.
  DOI: 10.1504/IJSTRUCTE.2021.10040392