Tariq Ali, Muhammad Sarmad Mahmood, Hawreen Ahmed
et al.
Abstract The construction industry is experiencing significant difficulties connected to construction and demolition waste management and its carbon footprint reduction. In reaction to this, a systematic literature review was conducted, which summarized information on 124 peer-reviewed studies measuring the accelerated carbonation of recycled concrete aggregates (RCAs). The aim of the review was to enhance the performance of RCA by sequestration of CO2, as well as to measure the resulting effects on the properties of recycled aggregate concrete (RAC), such as micro-crack healing and improvement of mechanical strength, durability and sustainability. Peer-reviewed articles were chosen according to their relevance to RCA carbonation and independence, and an independent screening and critical evaluation were used to reduce bias, and the synthesis of the extracted data was conducted in the narrative, which illuminated existing trends and comparisons between studies. The review examined four carbonation modalities including standard, pressurized, flow-through, and wet carbonation and assessed the effect of the most significant parameters on the results of the strengths and durability including relative humidity, temperature, CO2 concentration, and carbonation duration. Relative humidity was defined as 50–70%, a temperature between 20 and 30 °C and a concentration of CO2 of 20–50%, which together had the best carbonation rate and overall performance. The analyses reveal that carbonation enhances significantly the micro-crack healing, mechanical properties, and durability of RCA, and consequently, the quality of RAC is improved with respect to compressive strength, water absorption, and density. The best benefits were accrued by smaller RCA particles, which can be explained by a larger reactive surface area.
Systems of building construction. Including fireproof construction, concrete construction
Sayed Behzad Talaeitaba, Rasool Masoomi, Amir Behravan
et al.
Abstract This study evaluates the mechanical properties and durability of self-compacting lightweight concrete (SCLC) made with LECA lightweight aggregate with the addition of Forta and steel fibers in a comprehensive study. For this purpose, mechanical property tests such as compressive strength, flexural strength, and shear strength were performed, and durability indices in 10% magnesium sulfate, sulfuric acid, and chloride environments were studied. The results showed that SCLC structures containing Forta and steel fibers can be produced with a density of 1372–1468 kg/m3. According to the results, when Forta and steel fibers were added, the flexural strength increased by 47.37% and 66.32%, respectively, compared to the design without fibers. In addition, the flexural strength increased by 47 and 41 times with the addition of fibers, respectively. By adding Forta and steel fibers, the shear capacity of concrete increased by 31.05% and 26.12%, respectively, and the shear failure of the samples changed from brittle and brittle to ductile. Regarding durability indicators, the addition of Forta fibers and steel fibers can increase water absorption by 25.25% and 8.78%, respectively. After 750 days in a sulfate environment, samples containing Forta and steel fibers experienced a smaller decrease in compressive strength of 17.7% and 20.8%, respectively, while the sample without fibers showed a decrease in compressive strength of 33.2%. Also, the use of fibers reduced the damage against sulfuric acid attack, such that the control sample experienced a decrease in compressive strength of 19.92% after exposure to this environment, while in the samples with 0.6% Forta and steel fibers, this reduction was 17.10% and 15.30%, respectively.
Systems of building construction. Including fireproof construction, concrete construction
Sultan I. Akhmedov, Nodir A. Mukhamedov, Sayera R. Akhunzhanova
et al.
The article considers some of the possibilities of creating fire-retardant materials of a wide profile for concrete and reinforced concrete as well as for facing and finishing materials. Specific ways of practical application of new developments are given.
Systems of building construction. Including fireproof construction, concrete construction
Abstract To ensure the stability of interior beam-column joints under seismic loads, various influencing factors are incorporated into current design criteria in different countries. However, the design concepts and the influencing factors reflected in each country are different. The bond characteristics of beam longitudinal rebar penetrated the joint are mainly influenced by the compressive strength of concrete and are presented in the form of average bond stress. In Part I, the effect of concrete compressive strength on the bond characteristics of beam longitudinal rebar was directly investigated through a bond test that directly simulated the stress state of the joint. In this study, factors affecting the bond strength and required column depth were proposed by considering the bond characteristics based on the column axial force ratio and the yield strength of the beam longitudinal rebar. The experiment involved producing 14 test specimens and performing cyclic loading, taking each variable into consideration. Based on the experimental results, the proposed equation for the effect of column axial force ratio on the bond strength showed an excellent prediction performance compared to the current design equation with a coefficient of variation of 30.7%. In addition, a bond stress equation that reflects the stress difference of the beam longitudinal rebar was proposed using the strain values measured at both ends of the joint.
Systems of building construction. Including fireproof construction, concrete construction
Abstract This investigation addresses the notable gap in understanding the effects of fiber hybridization on concrete performance. The study's primary objective is to enhance the mechanical characteristics of high-strength concrete by incorporating a blend of steel and synthetic fibers. A detailed examination of 192 specimens, categorized into eight distinct groups, was conducted. This analysis focused on the roles of macrosteel and PP fibers in preventing significant cracks and micro-PVA and PP fibers in managing smaller-scale cracking. These specimens underwent stringent testing processes to evaluate the impact of fiber content, limited to a 1% concentration for macrofibers, on the compressive strength (CS) and flexural tensile (FTS) strength of the concrete. The results reveal that integrating steel fibers into concrete mixtures marginally enhances the CS (typically by 4–8%). In contrast, the incorporation of microsynthetic fibers (namely, PVA and PP), was observed to decrease the CS. This finding underscores the complexities inherent in the interaction between fibers and concrete. To support these findings, the study employed advanced nonlinear modeling techniques, concentrating on the interplay between various fiber types and their contributions to concrete strength. The developed models exhibit considerable predictive accuracy. The models showed the significant effect of macro-PP fibers on CS, especially when combined with steel fiber of length 40 mm. This specific blend produces a synergistic effect, notably enhancing the concrete's strength. Overall, this research provides crucial insights into the optimization of fiber-reinforced concrete mixtures, advancing the field by proposing enhanced mechanical performance strategies.
Systems of building construction. Including fireproof construction, concrete construction
Seleem S. E. Ahmad, Mohamed Yones, Mahmoud Zaghlal
et al.
Abstract An experimental program was conducted to study the eccentric behavior of columns reinforced with glass fiber-reinforced polymer (GFRP), steel bars, or a hybrid of both. Two strengthening methods were employed: GFRP mats and near surface-mounted (NSM) GFRP bars. Eighteen specimens with different reinforcement configurations, all having slenderness ratios 19, were tested under axial compression loads with eccentricities of 0.0 mm, 30 mm, and 60 mm. Results showed that using GFRP bars as longitudinal reinforcement significantly decreased the axial bearing capacity as eccentricity increased, with reductions of about 43% at 30 mm and 71% at 60 mm without additional strengthening. Specimens strengthened with three layers of GFRP mats exhibited reductions of approximately 35% and 56% at the same eccentricities, while a combination of GFRP mats and NSM bars showed reductions of 19% and 49%. At zero eccentricity, NSM GFRP rebars combined with GFRP wrap increased the loading capacity by about 10% and enhanced ductility by approximately 54%. Combining NSM GFRP rebars and GFRP wrap can significantly increase the loading capacity and improve displacement ductility. The obtained results show that these specimens outperform others. For example, the axial load is increased by 10% at e = 0, by 56% at e = 30, and by 93% at e = 60 compared to the control specimens. The elastic stiffness was comparable for columns reinforced with GFRP and steel. Using GFRP for longitudinal reinforcement and steel for stirrups resulted in a 16% reduction in axial load and a 22% reduction in axial displacement. The strengthening techniques proved more effective as the loading eccentricity approached the P–M curve’s equilibrium point.
Systems of building construction. Including fireproof construction, concrete construction
Jehan H. Aly, A. Farghal Maree, Mohamed Kohail
et al.
Abstract The bond between prestressing strands and concrete within the dead-end zone of a post-tensioned concrete member significantly influences the effectiveness of the strand-concrete system. However, the existing code equations for determining development length rely on studies conducted on pretensioned concrete members rather than post-tensioned ones. As a result, the implementation of development length for prestressing strands with bulb-shaped dead end anchorage in post-tensioning slabs relies on common practice and former experience. Unfortunately, this can sometimes lead to concrete cracks or strand slippage at the dead end zone due to insufficient development length. This paper presents an experimental study on post-tensioning slab segments representing the dead end zone. The aim of this study is to assess the development length of prestressing strands with bulb-shaped dead end that shall guarantee full bond with concrete throughout the member’s service life. The Specimens were divided according to three different concrete compressive strengths 34 MPa, 48 MPa and 70 MPa. The parameters considered included slab thicknesses of 160 mm and 250 mm, as well as strand embedment lengths of 700 mm and 850 mm. Based on the test results, the sufficient development length was determined. Furthermore, a verification was carried out to assess the validity of applying predicted equations from an adopted bond model to determine the bond strength of strand with bulb-shaped dead end anchorage in concrete slabs.
Systems of building construction. Including fireproof construction, concrete construction
Ana I. Sarkis, Timothy J. Sullivan, Emanuele Brunesi
et al.
Abstract Even if precast pre-stressed hollow-core (PPHC) slabs are usually designed as simply supported elements, continuity with the supporting beam may exist when constructed together with a reinforced concrete topping and continuity reinforcing bars. During an earthquake (and possibly other lateral load), this continuity may result in bending moments being induced close to the supports as the buildings sway laterally. The response of precast floors to earthquake-induced demands has been addressed by past research. However, further investigation is required to improve understanding of several aspects of precast floor behaviour either revealed or emphasized by recent earthquakes in New Zealand. This paper proposes a mechanics-based modelling approach for the analysis of PPHC slab-to-beam seating connections. The model has been calibrated against existing test data to predict the failure of a PPHC slab under negative bending moments. The numerical outcomes allow comparison of the moment–drift response, principal tensile stresses, and crack progression during loading. The developed modelling approach will allow future studies to exhaustively investigate all aspects of precast floor behaviour by varying the properties and geometry of the PPHC seating connection.
Systems of building construction. Including fireproof construction, concrete construction
Abstract Accelerated bridge construction (ABC) has many advantages for bridge construction in modern society. While for ABC, the post-cast joint is always the weakest and most critical part. This paper presents a UHPC rhombus-strip-shaped (RSS) joint suitable for ABC. Several model tests were carried out to verify its resistance to flexural and shear. First, large-scale model tests are advanced to confirm its flexural properties. The results show that densified and welded joint interface rebars can significantly improve the ultimate bearing capacity and durability-based cracking stress of the RSS joint beams, and the ultimate bearing capacity can reach 90% of the complete beam. Then the shear-resistance tests were carried out. The results show that the UHPC RSS joint beam has excellent bending-shear mechanical properties and better ductility. Lastly, the ultimate flexural bearing capacity and shear-resistance capacity calculation methods were obtained.
Systems of building construction. Including fireproof construction, concrete construction
Wameedh Ghassan Abdul Hussein, Ahlam Sader Mohammed, Mohammed Elwi
In this study, the effectiveness of the structure of a tall building (consisting of nineteen floors) was analysed and investigated by the existence or absence of shear walls (SW) to resist loads of wind and earthquake effect. Note that each floor contains four apartments comes under zone 2 Four different styles of shear walls were used in terms of shape and location. The results were analysed and discussed for each case and for each floor, and comparisons were made between those results in terms of (moments, lateral forces, vertical loads, and torsion moments). There are several techniques for solving structural engineering problems, and one of those distinct techniques is the design optimization techniques method. The most complicated high-rise buildings that use design optimization, which includes each of size and topological optimization, are addressed by considering stability, safety, and responsiveness to various sorts of loadings A project includes wall-frame structural optimization. When this wall and core system was subjected to various loadings, it was tested for displacement, internal stresses, and intensities. The SAP2000 Software has made design improvements to the construction of the reinforced concrete plane frame to minimize the costs to beams and columns of the concrete and steel by Using a computer model called an Artificial Neural Network (ANN). The concept method is in accordance with ACI-318-08 Code. To improve the design optimization, many variables have been used depth, width, and the steel reinforcing area Including both (longitudinal and shear reinforcement). It can be concluded that by putting the shear walls nearest the structure geometric center the best performance of seismically loaded structure can be achieved; the maximum displacement, bending moment horizontal forced, and torsional moments were decreased.
Ensuring safety during work at height is the most important task in the context of the development of a modern construction complex. Falling from a height occupies one of the first places in terms of the number of victims among all the traumatic factors, based on the statistical data, and its share among other traumatic factors is 28 %. Works at height include construction works, in which there are risks associated with a possible fall of an employee from the height of more than 1.8 m. The employer is obliged to ensure the implementation of measures to reduce injuries at the construction site in accordance with the current legislation. Protective measures when working at height include personal and collective protective equipment, including the use of anchor lines on the building roofs. The article provides for a comparative analysis of five options for the installation of anchor lines suitable for wooden, concrete, metal, and green roofs. For the analysis, a flexible anchor line using a metal cable, a rigid anchor line on high supports, a rigid anchor line on low supports, a flexible anchor line with weights for use on the roofs with landscaping and a flexible anchor line with supports were selected. All the selected anchor line systems comply with the international safety requirements and can be used by one or more workers. The advantages of each system of the anchor lines are revealed, a wide variety of roofing materials are considered: metal seam, made of polyvinyl chloride, with oriented strand board and thermoplastic polyolefin reinforced membrane, which is a high-tech polymer roofing material. All the anchor lines have a variability in terms of the shape and can be used on the roofs of any configurations in the building design without additional efforts and search for the complex solutions on the part of the designer.
Abstract The linear complementarity problem (LCP) approach, expedited by using the simple rigid–plastic theory, has been utilized successfully in predicting the numerical response of the ductile steel or concrete structures subjected to short-duration, high-intensity dynamic loads. The current study attempts to improve the computational stability of this powerful technique while determining the response of skeletal structures under blast loading. The performance of the Lemke LCP solver is amplified by introducing an automatic time-stepping scheme to efficiently trace the complex dynamic response using either lumped mass or continuous mass discretization. The computational efficiency of this solver is tested against carefully chosen three numerical examples, and the acquired results are in good agreement with the derived closed-form solution and results from other sources.
Systems of building construction. Including fireproof construction, concrete construction