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Reinforced concrete structures, particularly in cold areas, experience early deterioration due to steel corrosion. Fiber-Reinforced Concrete (FRC) is an emerging construction material and cost-effective substitute for conventional concrete to enhance the durability and resistance against crack development. This article examines the structural performance of hybrid ferro fiber reinforced concrete slabs (mix ratio of mortar 1:2) comprising silica fume, layers of spot-welded mesh and different ratios of polypropylene fibers. The ferrocement slabs are compared with a conventional Reinforced Cement Concrete (RCC) slab (mix ratio of 1:2:4). The experimental work comprised a total of 13 one-way slabs, one control specimen and three groups of ferrocement slabs divided based on different percentages of Poly Propylene Fibers (PPF) corresponding to 0.10%, 0.30% and 0.50% dosage in each group. Furthermore, in each group, the percentage of steel ratio in ferrocement slabs varied between 25% and 100% of the steel area in the reinforced concrete control slab specimen. For evaluating the structural performance, the observation of deflection, stress-strain behavior, cracking load and energy absorption are critical parameters assessed using LVDTs and strain gauges. At the same time, the slabs were tested in flexure mode with third point loading. The experimental results showed that the first cracking load and ultimate deflection for fibrous specimens with 0.5% fiber and 10% silica fume increased by 15.25% and 13.2% compared with the reference RCC control slab. Therefore, by increasing the percentage of PPF and steel wire mesh reinforcement in the ferrocement slab, the post-cracking behavior in terms of deflection properties and energy absorption capacity was substantially enhanced compared to the RCC control slab. [ABSTRACT FROM AUTHOR]

Lightweight clay aggregate (LECA) is manufactured by heating clay with no lime content in the kiln; as a result, the water evaporates and angular clay balls with pore structures are obtained. LECA possess internal curing properties as any other lightweight aggregate due to their pore structure and higher water absorption capacity. In this work, experimental and analytical behaviour using LECA as a 100% replacement for coarse aggregate to make lightweight concrete (LWC) beams was studied. The LWC beams were compared to the conventional concrete beams in load-deflection, energy absorption capacity, and ductility index. Internal mesh reinforcement using welded wire mesh (WWM) of (4 layers of 15 mm square spacing, 4 layers of 10 mm square spacing, and 4 layers of 15 mm and 10 mm mesh placed alternatively) was provided to enhance the load-carrying capacity of the LWC beam without increasing the dimensions and self-weight of the beams. The beam internally reinforced with WWM exhibited higher load carrying capacity and withstood more significant deflection without sudden failure. The internal reinforcement of WWM is provided to make steel rebars, and WWM works monolithically while loading; this will reduce the stress on tension bars and increase load-carrying capacity. Finally, the generated analytical findings agreed well with the experimental data, demonstrating that the analytical model could mimic the behaviour of LWC beams with WWM. [ABSTRACT FROM AUTHOR]

Beam–column joints are extremely vulnerable to lateral and vertical loads in reinforced concrete (RC) structures. This insufficiency in joint performance can lead to the failure of the whole structure in the event of unforeseen seismic and wind loads. This experimental work was conducted to study the behaviour of ternary blend geopolymer concrete (TGPC) beam-column joints with the addition of hybrid fibres, viz., steel and polypropylene fibres, under reverse cyclic loads. Nine RC beam-column joints were prepared and tested under reverse cyclic loading to recreate the conditions during an earthquake. M55 grade TGPC was designed and used in this present study. The primary parameters studied in this experimental investigation were the volume fractions of steel fibres (0.5% and 1.0%) and polypropylene fibres, viz., 0.1 to 0.25%, with an increment of 0.05%. In this study, the properties of hybrid fibre-reinforced ternary blend geopolymer concrete (HTGPC) beam-column joints, such as their ductility, energy absorption capacity, initial crack load and peak load carrying capacity, were investigated. The test results imply that the hybridisation of fibres effectively enhances the joint performance of TGPC. Also, an effort was made to compare the shear strength of HTGPC beam-column connections with existing equations from the literature. As the available models did not match the actual test results, a method was performed to obtain the shear strength of HTGPC beam-column connections. The developed equation was found to compare convincingly with the experimental test results. [ABSTRACT FROM AUTHOR]

Self-sensing concrete is a smart material known for its cost-effectiveness in structural health-monitoring areas, which converts the external stimuli into a stress/strain sensing parameter. Self-sensing material has excellent mechanical and electrical properties that allow it to act as a multifunctional agent satisfying both the strength and structural health-monitoring parameters. The main objective of this review is to understand the theories and principles behind the self-sensing practices. Many review papers have focused on the different types of materials and practices that rely on self-sensing technology, and only a few articles have discussed the theories involved. Understanding the mechanism and the theories behind the conduction mechanism is necessary. This review paper provides an overview of self-sensing concrete, including the principles such as piezoresistivity and piezopermittivity; the tunnelling effect, percolation threshold, and electrical circuit theories; the materials used and methods adopted; and the sensing parameters. The paper concludes with an outline of the application of self-sensing concrete and future recommendations, thus providing a better understanding of implementing the self-sensing technique in construction. [ABSTRACT FROM AUTHOR]

Past historical earthquake events from neighbouring countries have been proven to be disastrous. Building in the aftermath of an earthquake may reduce structural reliability, posing risk upon re-occupation of the building. Shock absorber viscous dampers were installed on a specific structure storey that could reduce the spectral acceleration and storey-drift caused by an earthquake. The research object is a low-rise, three-storey, reinforced concrete (RC) structure. This study aims to identify the dynamic response of the scaled RC structure with and without attached dampers and performs structural reliability of the tested model under the excitation of Peak Ground Acceleration (PGA) of 0.1 g to 1.0 g with a unidirectional shaking table. APIDO viscous dampers were installed parallel to the movement direction of the dynamic load test. The findings show the scaled model with attached viscous dampers reduces spectral acceleration and storey drift by 9.66% and 4.85%, respectively. Findings also show the change of the structural behaviour from single curvature to double curvature due to the increase in seismic structural resistance by viscous dampers. The breakthrough of this research shows that structural reliability analysis performed by the Weibull distribution function has a base shear capacity increment of 1.29% and 6.90% in seismic performance level Life Safety (LS) and Collapse Prevention (CP), respectively. The novelty of this case study building with dampers managed to increase the building's base shear and roof shear capacity by 6.90% and 16% compared to the building without dampers under dynamic load excitation. [ABSTRACT FROM AUTHOR]

This research presents a novel approach of artificial intelligence (AI) based gene expression programming (GEP) for predicting the lateral load carrying capacity of RC rectangular columns when subjected to earthquake loading. To achieve the desired research objective, an experimental database assembled by the Pacific Earthquake Engineering Research (PEER) center consisting of 250 cyclic tested samples of RC rectangular columns was employed. Seven input variables of these column samples were utilized to develop the coveted analytical models against the established capacity outputs. The selection of these input variables was based on the linear regression and cosine amplitude method. Based on the GEP modelling results, two analytical models were proposed for computing the flexural and shear capacity of RC rectangular columns. The performance of both these models was evaluated based on the four key fitness indicators, i.e., coefficient of determination (R2), root mean squared error (RMSE), mean absolute error (MAE), and root relative squared error (RRSE). From the performance evaluation results of these models, R2, RMSE, MAE, and RRSE were found to be 0.96, 53.41, 38.12, and 0.20, respectively, for the flexural capacity model, and 0.95, 39.47, 28.77, and 0.22, respectively, for the shear capacity model. In addition to these fitness criteria, the performance of the proposed models was also assessed by making a comparison with the American design code of concrete structures ACI 318-19. The ACI model reported R2, RMSE, MAE, and RRSE to be 0.88, 101.86, 51.74, and 0.39, respectively, for flexural capacity, and 0.87, 238.74, 183.66, and 1.35, respectively, for shear capacity outputs. The comparison depicted a better performance and higher accuracy of the proposed models as compared to that of ACI 318-19. [ABSTRACT FROM AUTHOR]

Manufacturers of building materials strive to optimize the three basic concrete properties—strength, durability, and shrinkage deformation, of which the focus is generally on the durability in the structure when designing and monitoring the poured concrete. Studying concretes' structural performance and the change in their characteristics over time enables the solution of many important issues associated with the design of reliable, durable, and cost-effective buildings and structures. This article presents studies aimed at improving the physical, technical, and operational characteristics of cement concrete and reducing cement consumption in heavy concretes through the use of complex modifiers and volumetric fiber reinforcement. Four concrete compositions of widely recognized grades were developed, of which samples were molded and tested for compressive and flexural strength, frost resistance, volumetric water absorption, and density. Test results confirmed the possibility of binder (cement) economy up to 18% and increasing frost resistance up to W300 when using microsilica, reduction in volumetric water absorption of up to 40% when using both microsilica and hyperplasticizer, and increasing flexural strength by over 30% when using polymer fiber. The developed compositions passed the industrial tests, and were successfully introduced in the production process of the operating reinforced concrete products' manufacturer. [ABSTRACT FROM AUTHOR]

The stress values at the crack tip in bending reinforced concrete beams are considered. The stress state is analytically determined with an initial and propagating crack. Equations of the equilibrium of a part of the beam cut along the crack line are compiled. These equations are reduced to a system of two nonlinear algebraic equations using the plane-sections hypothesis. The equations determine the stress zone's height and the nominal stress at the crack tip for a beam with an initial crack and the crack length. The rest of the stress state parameters are expressed regarding the zone stress height and the nominal stress or crack length. The same equation system determines the external moment starting from which the crack length increases. The analytical method for determining the stress intensity factor (SIF) with an initial and growing crack in bent reinforced concrete beams is proposed. The method is based on the assumption that the size of the stress concentration zone at the crack tip is determined by the equality of the nominal and local stresses at the end of this zone. The method determines the value of the external moment starting from which the crack length increases. The stress zone's size is determined by the coincidence of the local stress with the nominal stress. The same problem is solved in a three-dimensional formulation by the FE method, considering the stress field's peculiarities at the crack tip. The calculation results coincide with the analytical solutions. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) provides an opportunity to assess and predict changes in the technical condition of structures during the operation of a building. Structural damage, as well as several operational and environmental conditions, causes changes in modal parameters. Temperature is the most popular environmental condition which is used for research. However, to the authors' knowledge, this is the first investigation that highlights the effect of groundwater level change on the natural frequencies of the buildings and the impact of possible damage detection features. Groundwater level change can influence structural health monitoring measurements and cause faulty structural damage identification using vibration-based methods. This paper aims to analyse the impact of the groundwater level changes on the modal parameters of mid-rise reinforced concrete buildings. The modal parameters of mid-rise reinforced concrete buildings are determined using finite element (FE) models. Three different FE models of structural system types of nine-storey reinforced concrete (RC) buildings with shallow foundations are used to determine the impact of groundwater level fluctuation on the values of the buildings' natural frequencies. Changes in the groundwater level have an impact on the natural frequencies of the mid-rise reinforced concrete buildings. This research proposes a new environmental condition that has to be considered to identify the structural damage using the vibration-based method. It is found that groundwater level rise causes a decrease in the natural frequency value. In this research, it is established that the influence of the groundwater level on the natural frequencies of the buildings can change abruptly, and there is a non-linear correlation between groundwater level change and natural frequencies of the buildings. The natural frequencies of the buildings can change under varying environmental conditions as well as in the case of structural damage. To identify structural damage in the long-term structural health monitoring measurements, it is recommended to select features which are sensitive to structural damage but are not affected by groundwater level change. Data normalisation and elimination using linear correlation methods can be used for short-term SHM under varying seasonal groundwater level change. [ABSTRACT FROM AUTHOR]

The research object was three-layer reinforced precast concrete enclosure structures. The structures consist of heavy concrete B25 in the external layers and polystyrene concrete B1 in the internal layer. The stress–strain state of precast concrete structures during crack formation was studied by considering the influence of contact interlayers between different types of concretes. Stereoscopic microscopy and scanning electron microscopy were used in the experimental study of multilayer concrete blocks. Samples were made with a varied break time from 30 min to two hours between the previous and the next concrete layer placings. The experimental results showed that the contact interlayer with mutual penetration of aggregates into the adjacent concrete layers is formed in the successive layer-by-layer placing of various concretes. The thickness of the contact interlayer was up to 1 cm. The contact interlayer affects the solidity of the concrete layers' connection and the structure's stress–strain state. A model and method for calculating cracking in three-layer reinforced concrete structures with contact interlayers based on analytical and numerical calculations are proposed. Experimental data confirm the proposed calculation method. The results of three-layer reinforced concrete beams calculations show that: (i) the difference of the moment during crack formation in three-layer reinforced concrete beams schemes with and without taking into account the contact interlayer can reach 9.9%; (ii) the moment during crack formation obtained according to the proposed method is greater than that obtained according to the scheme of the cross-section conversion from 7.4% to 9.1%. [ABSTRACT FROM AUTHOR]