فهرست مطالب

Rehabilitation in Civil Engineering - Volume:12 Issue: 4, Autumn 2024

Journal of Rehabilitation in Civil Engineering
Volume:12 Issue: 4, Autumn 2024

  • تاریخ انتشار: 1403/03/16
  • تعداد عناوین: 9
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  • Kamel Akroum *, Bouzidi Mezghiche Pages 1-19
    The use of demolition aggregates (DAs) in second-generation concretes is an important issue, as they often have high water absorption, which affects the workability and durability of the cementitious materials incorporating them. This makes their direct use in structural concrete impossible. Previous studies have focused on downstream interventions aimed at improving the quality of DAs, such as eliminating old mortar (OM) adhered to natural aggregates (NAs) or limiting its absorption capacity. However, these approaches have proven to be expensive, time-consuming, and, for some, have health consequences. Our objective was to produce DAs suitable for use in structural concrete and to develop a simple, economical, and safe technique to generate good-quality DAs. We designed an upstream intervention based on the measurement of water absorption as a quality indicator. Seven ordinary concretes served as parent concretes (PCs), and after 28 days of maturation, the PC specimens were divided with a metal mass and then separated into ten different subfractions using standardized sieves. Three representative samples per subfraction were subjected to a twenty-minute water absorption evaluation, resulting in seventy arithmetic averages over 210 trials. Fractions (3/8), (8/16), and (16/25) were produced by clustering DA subfractions while emulating the granular distributions of NAs. The calculation of the DA fractions' water absorption was done based on the individual measurements obtained earlier. In the end, 21 average values were emerged. The maximum diameter of each DA (DADmax) was related to that of the NA of its parent concrete (NADmax), making it easier to distinguish between the most and least absorbent DAs. The ratios of 0.8 for the DA sub-fractions and 1 for the reconstituted DA fractions corresponded to DAs with the lowest water absorption capacity. For the DA sub-fractions, the minimum values are 12% to 82% below the average values and 28% to 89% below the maximum values. Similarly, DA fractions reconstituted from DA sub-fractions of the same PC showed a decrease in minimum values of 21% to 43% compared to average values and 31% to 58% compared to maximum values. Selecting the least absorbent DA sub-fractions without taking the PC into account resulted in a further reduction of 4% to 7% compared with the minimum values. The DADmax/NADmax ratio can therefore be used as a production and selection criterion for demolition aggregates.
    Keywords: Demolition Aggregates, Natural Aggregates, Quality Indicator, Dadmax, Nadmax Ratio, Water Absorption Capacity
  • Mohammadjavad Akhavanbahabadi, Mohammad Khabiri * Pages 20-31
    The widespread application of bitumen emulsion, especially in surface treatment as the commonest approach to road maintenance in the world, indicates the necessity of finding ways to improve the bitumen emulsion performance. The present research is aimed at investigating the effect of polyphosphoric acid (PPA), as an admixture, on rheological characteristics of the bitumen emulsion. For this purpose, PPA was used at different dosages (i.e., 0.4, 0.8, 1.2, and 1.6 wt.% by weight of the residual bitumen emulsion) to modify the bitumen emulsion. Evaluation of the modified bitumen emulsion samples was performed based on a number of physical parameters (Saybolt Furol viscosity, softening point, penetration, and thermal sensitivity) and dynamic shear rheometer (DSR) and multiple stress creep recovery (MSCR) tests. Results of the bitumen tests showed that the use of PPA improved the bitumen emulsion characteristics in terms of reduced penetration, increased softening point, and decreased thermal sensitivity. With increasing the PPA dosage to up to 0.8 wt.% by weight of residual bitumen emulsion, the resultant changes in the penetration and softening point were significant and improved the bitumen emulsion performance. It was also observed that the value of G*/sin ( ), as a measure of resistance to bleeding in hot weather, increases with PPA dosage in all samples, with the best performance obtained with the samples containing PPA at 0.8 and 1.2 wt.%. An increase in the operating temperature of the PPA-modified samples was seen, so that the sample containing PPA at 0.8 wt.% exhibited 28.6% higher operating temperature than the control sample. The values of R% and %Rdiff parameters increased with the PPA dosage. The observed reduction of percent recovery due to increased temperature in the modified sample indicated the lower sensitivity of the modified bitumen emulsion to temperature rise. The value of Jnr parameter decreased with increasing the PPA dosage, indicating a boost in the resistance of the bitumen emulsion to bleeding.
    Keywords: Bitumen Emulsion Modification, Rheological Characteristics, Polyphosphoric Acid (PPA), Bleeding, Microsurfacing
  • Investigation of double layer corrugated steel plate shear walls in multi-story frames
    Mahdi Kiani, Ali Mohammad Rousta *, Hamed Enatyati Pages 32-54
    Flat steel plate shear walls (FPSWs) are widely used in steel structures, but they are prone to buckling under lateral loads. As an alternative, corrugated steel plate shear walls (CPSWs) have been introduced, in which the infill flat steel plate is replaced with a corrugated steel plate. CPSWs have some advantages over FPSWs, such as improved in-plane and out-of-plane stiffness, buckling strength, and ductility. Nevertheless, their applicable thickness is limited due to manufacturing capabilities. In the last few years, to overcome this drawback, double-layer corrugated steel plate shear walls (DCPSWs) composed of two similar corrugated steel plates have been developed. As there are few studies on DCPSWs, mainly focused on single-story frames, this paper considers 48 two-dimensional multi-story frames with DCPSWs using the pushover method. According to the results, corrugated shear walls have less lateral strength compared to FPSWs. However, the difference decreases with increasing the number of stories. The corrugated shear walls have higher ductility, especially for low-rise frames. Furthermore, the frames with DCPSWs experienced the highest inelastic deformations, which can be considered an advantage over CPSWs.
    Keywords: Corrugated Steel Plate Shear Walls, Double-Layer Corrugated Steel Plate Shear Walls, Multi-Story Frames, Building Technology, Seismic Retrofitting
  • Compressive strength of recycled green concrete affected by chloride and sulfate exposures
    Md.Roknuzzaman, Md .Rahman * Pages 55-65

    The use of recycled aggregate to make concrete is a viable option to minimize demolition waste load in landfills and to preserve the natural resources of aggregates. Several studies reveal the potential of recycled aggregates, which can be re-used in concrete, resulting in green concrete with acceptable strength parameters. However, the performance of green concrete under adverse exposure conditions is yet to be evaluated on a larger scale. The present study investigates the compressive strength of green concrete under chloride and sulfate exposure. C-20-grade concrete specimens are prepared using recycled coarse aggregates derived from demolished concrete blocks from an 8-year-old highway culvert. After 28 days of regular water curing, the specimens are subjected to chloride and sulfate environments by immersing them in chloride and sulfate solutions. Compressive strength tests are conducted after 28 days, 56 days, 84 days, and 112 days of immersion. The results are compared with normal concrete of the same composition. Green concrete is found to be more susceptible to salt attacks than regular concrete. Sulfate exposures happen to be more damaging compared to chloride exposures. A maximum of 36.73% loss of compressive strength is encountered for 112 days of immersion of specimen in 10% 〖"Na" 〗_"2" "S" "O" _"4" solution. The study recommends that caution should be taken while using recycled concrete in chloride and sulfate-prone environments.

    Keywords: Green Concrete, Sulfate Attack, Chloride Attack, Recycled Aggregate
  • Evaluation of Steel Frame Equipped with the Replaceable Shear Link Made of Shape Memory Alloy under the Impact Load
    Reza Kamgar *, Seyed Ali Mahmoudy, Roham Zakavi Pages 66-85
    Despite their low stiffness, moment frames (MFs) are considered conventional lateral strength systems for low- and moderate-rise structures due to their ability to absorb energy and provide suitable ductility, along with architectural considerations. In return, a framed tube system with deep beams and short spans suits the high-rise structures. Due to the differences between the span length-to-depth ratios of the beams in this structural system, the regulations for MFs cannot apply to them. Moreover, a low value for the length-to-height ratio of the beams prevents the proper formation of flexural plastic joints proposed by the regulations. Therefore, a frame with a single story and span has been proposed here consisting of a replaceable shear link made of shape memory alloy (SMA) to study the responses of the structure under the explosive loads (i.e., lateral loading) that can occur due to terrorist attacks, industrialization, or mining actions. Therefore, this study investigates the behavior of different systems under the three types of impact loads, including SMA or steel shear links. The results show that in the frame equipped with a shear link made of an SMA, the base shear is less than that of ordinary steel (the maximum base shear reduction is about 27% for type 2 blast load). This leads to a reduction in the cost of foundation construction. Also, the maximum displacement in the frame equipped with the shear link made of ordinary steel is less than the corresponding value in the frame equipped with a shear link made of an SMA (the maximum displacement reduction is about 43% for type 1 blast load), while the residual displacement of both frames is the same and equal to zero. It was concluded that the free vibration does not significantly affect the maximum responses of the mentioned structures under the impact load.
    Keywords: Impact Load, Shear Link, Framed Tube, Shape Memory Alloy, Nonlinear Dynamic Analysis
  • Mostafa Farajian *, Mohammadiman Khodakarami Pages 86-102

    The use of pre-fabricated modular units for the construction of mid to high-rise buildings has been promoted recently. The modular units are fabricated in a factory and then transported to the construction site to form a structure using inter-connections. The inter-connection is unique to modular buildings, playing a critical role in their structural performance. Despite the increasing popularity of modular construction, there are relatively few published studies considering the influence of inter-connection’s behaviour on the lateral performance of braced-frame modular buildings. The inter-connections’ rigidity has an influence on the modular buildings’ stiffness. Hence, it is required to investigate their effect on the seismic performance of braced-frame modular buildings. This study aims to investigate the effect of inter-connections’ properties on the lateral performance of braced modular frames through nonlinear static analysis. To that end, three frames of four, eight and twelve storeys, are assumed for the required analysis. Different inter-connections having various stiffness properties are considered for the nonlinear static analysis. Three performance levels are considered and the responses of considered structures at these levels are evaluated and compared for different properties of inter-connections. The obtained responses indicate that the decrease of inter-connections’ stiffness leads to reduction of the lateral capacity. The results indicate that the decrease of inter-connection stiffness can increase the period of the structures up to 10.35%., 5.35% and 3.63% in 4-, 8- and 12-storey buildings. Moreover, the nonlinear analysis indicate that the increase of inter-connection flexibility reduces the base shear by 1.9%.

    Keywords: Inter-Modular Connections, Seismic Performance, Modular Buildings, Pushover Analysis, Stiffness
  • Kamel Kamel *, Ahmed Amer, Ahmed Hanafi Pages 103-115
    The main objective of this study is to make a comparison between calculating live load distribution factors using AASHTO-LRFD equations and the finite element analysis of precast concrete U-girder bridges. The AASHTO-LRFD specifications provide empirical equations for calculating the distribution factors. Little information is available regarding the accuracy of these equations for this kind of bridge girder. As a result, an extensive parametric study was carried out using finite element modelling to evaluate the parameters that influence the live load distribution factors and to verify the accuracy of the AASHTO-LRFD equations to calculate these factors. The parameters considered in this study were bridge span, girder spacing, number of girders, and number of lanes. 52 prototype bridges were analysed using CSI Bridge software to determine moment and shear distribution factors due to the effect of the AASHTO-LRFD live load model (HL-93). All of the bridges studied were assumed to have straight and simply supported spans. According to the study''s results, the length of the girder does not affect the LLDF, while the parameters of the distance between girders, girder count, and lane count have a significant impact. In most cases, the AASHTO equations overestimate the calculated moment and shear distribution factors. Especially for wide bridges, the parametric study found that the difference between AASHTO equations and FEA results for calculating shear distribution factors was 87%. Consequently, it is best to avoid using these equations on wide bridges.
    Keywords: Live Load Distribution Factors, AASHTO Specifications, Finite Element Analysis, U-Girder Bridges
  • Ali Nikkhoo *, Amin Moshtagh, Mehri Mehrnia Pages 116-135
    The nonlinearity observed in high-performance concrete (HPC) can be attributed to its distinctive features. This study examines the effectiveness of expert frameworks in determining compressive strength, aiming to enhance accuracy through the development of a master artificial neural network (ANN) system utilizing the sonar inspired optimization (SIO) algorithm. The ANN model employs exploratory data to establish initial optimal weights and biases, thereby improving precision. Comparison with previous studies validates the accuracy of the proposed system, demonstrating that the SIO-ANN hybrid model offers finer estimation of high-performance concrete properties. Results consistently show a coefficient of determination (R2) exceeding 0.972 and a 50%-67% reduction in error rates compared to conventional fitting curve approaches. Parameters such as population, weight, and bias within the SIO-ANN framework are continuously updated and optimized to achieve optimal values efficiently. Additionally, the SIO-ANN model exhibits superior runtime performance compared to other models. Consequently, the proposed SIO-ANN approach emerges as a viable alternative for accurately assessing and predicting the compressive strength of high-performance concrete.
    Keywords: High-Performance Concrete, Sonar Inspired Optimization, Optimization, Artificial Neural Network, Prediction
  • Hamid Dehghani, Ehsan Dehghani *, Mehdi Sharifi, Seyed Rohollah Hoseini Vaez Pages 136-154
    The tension forces of cables in cable-stayed bridges during their construction and operation may differ from initial conditions, which could affect the amount and distribution of internal forces on other parts of the bridge. If some bridge elements are loaded to their yield limits, alternating plasticity and incremental collapse could occur under moving and repeated loading. This study investigated the effect of the initial tension force on the stiffness, strength, shakedown limit load, and alternating plasticity of cable-stayed bridges, which has not been studied so far. Two case study bridge models with cables having different initial forces were tested using nonlinear static analysis under gravitational force and nonlinear dynamic analysis under transient moving loads. The results showed that changes in the initial cable forces did not change the initial stiffness, ultimate strength, shakedown limit, alternating plasticity, or bridge reliability. These results were theoretically validated using plastic analysis theorems. This paper presents a new construction method for cable-stayed bridges based on the finding that adjusting the cable tension to the design value is not necessary during construction and operation. This method eliminates the need for tension adjustment and ensures that the final geometric shape of the bridge matches the expected profile. The proposed method offers a simpler and more efficient approach to constructing cable-stayed bridges without compromising the safety and durability of the structure.
    Keywords: Cable-Stayed Bridge, Shakedown Analysis, Alternating Plasticity, Incremental Collapse, Construction Analysis, Nonlinear Analysis