Research

25 pages, 2578 KiB

Open AccessArticle

Unified Flexural Resistance Design Method and Evaluation Frame for the B-Regions of RC Flexural Members—Theory and Application

by Yuguo Zheng, Yuqi Liao, Bin Kang and Minghang Chen

Buildings 2023, 13(5), 1138; https://doi.org/10.3390/buildings13051138 - 24 Apr 2023

Viewed by 1182

Abstract

The load and resistance factor design (LRFD) method is normally used to design B-regions of reinforced concrete (RC) flexural members. The design includes many checks corresponding to different limit states. The LRFD method requires many loop calculation steps in the design, demonstrating its [...] Read more.

The load and resistance factor design (LRFD) method is normally used to design B-regions of reinforced concrete (RC) flexural members. The design includes many checks corresponding to different limit states. The LRFD method requires many loop calculation steps in the design, demonstrating its relative inefficiency. It cannot be applied to compare limit states directly and quantitatively. Different design limit states are separated and isolated. How to improve the analytical calculation efficiency of the LRFD method and to realize direct and quantitative comparisons between limit states are very important problems in structural engineering. This paper presents an innovative unified flexural resistance design (UFRD) method and a unified flexural resistance evaluation (UFRE) frame to solve these problems to some extent. The main contents include the unified flexural resistance (UFR) principles, formulas for the unified flexural resistance design (UFRD) method, the operation procedure to facilitate its usage, the UFRE framework to compare limit states, and three examples. The results show that the UFRD method can provide the same design outcomes as the LRFD one. However, UFRD calculations are simpler, requiring at most 20% of the calculation steps of the LRFD method. The UFRE frame can make different limit states compare with each other directly and quantitatively, which cannot be realized by the LRFD method. It helps expose some potential and insufficient flexural resistance hazards for some limit states, such as the only 10% relative strength reservation of one example. Thus, the UFRD method and the UFRE frame supplement and develop the LRFD method to some degree. The simplicity and practicality of the approach and the frame make them appropriate for many applications. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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28 pages, 6292 KiB

Open AccessArticle

Optimization of Fresh and Mechanical Characteristics of Carbon Fiber-Reinforced Concrete Composites Using Response Surface Technique

by Muhammad Basit Khan, Ahsan Waqar, Naraindas Bheel, Nasir Shafiq, Nadhim Hamah Sor, Dorin Radu and Omrane Benjeddou

Buildings 2023, 13(4), 852; https://doi.org/10.3390/buildings13040852 - 24 Mar 2023

Cited by 31 | Viewed by 2067

Abstract

As a top construction material worldwide, concrete has core weakness relating to low tensile resistance without reinforcement. It is the reason that a variety of innovative materials are being used on concrete to overcome its weaknesses and make it more reliable and sustainable. [...] Read more.

As a top construction material worldwide, concrete has core weakness relating to low tensile resistance without reinforcement. It is the reason that a variety of innovative materials are being used on concrete to overcome its weaknesses and make it more reliable and sustainable. Further, the embodied carbon of concrete is high because of cement being used as the integral binder. Latest research trends indicate significant potential for carbon fiber as an innovative material for improving concrete mechanical strength. Although significant literature is available on the use of carbon fiber in concrete, a limited number of studies have focused on the utilization of carbon fiber for concrete mechanical strength improvement and the reduction of embodied carbon. Following the gap in research, this study aimed to investigate and optimize the use of carbon fiber for its mechanical characteristics and embodied carbon improvements. The use of carbon fiber in self-compacting concrete lowers sagging. The greatest quantity of carbon fiber is that it reduces the blockage ratio, forcing the concrete to solidify as clumps develop. With time, carbon fiber improves the durability of concrete. Self-compacting concrete with no carbon fiber has a poor tensile strength. Experiments were conducted by adding carbon fiber at 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% by weight. Fresh concrete tests including slump test and L-box test, hardened concrete tests involving compressive strength and splitting tensile strength, and durability tests involving water absorption and acid attack test were conducted. Embodied carbon ratios were calculated for all of the mix ratios and decreasing impact, in the form of eco-strength efficiency, is observed with changes in the addition of carbon fiber in concrete. From the testing results, it is evident that 0.6% carbon fiber is the ideal proportion for increasing compressive strength and split tensile strength by 20.93% and 59%, respectively, over the control mix. Response Surface Methodology (RSM) is then applied to develop a model based on results of extensive experimentation. Optimization of the model is performed and final modelled equations are provided in terms of calculating the impact of addition of carbon fiber in concrete. Positive implications are devised for the development of concrete in the future involving carbon fiber. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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18 pages, 10999 KiB

Open AccessArticle

Optimal Design of Segment Storage and Hoisting of Precast Segmental Composite Box Girders with Corrugated Steel Webs

by Qigang Song, Wenqin Deng, Duo Liu, Huiteng Pei, Zongqing Peng and Jiandong Zhang

Buildings 2023, 13(3), 801; https://doi.org/10.3390/buildings13030801 - 17 Mar 2023

Viewed by 1691

Abstract

To optimize the segment storage and hoisting plan of precast segmental composite box girders with corrugated steel web bridges, China’s first precast segmental composite girder bridge with corrugated steel webs is taken as the background. The difference between the precast segmental composite box [...] Read more.

To optimize the segment storage and hoisting plan of precast segmental composite box girders with corrugated steel web bridges, China’s first precast segmental composite girder bridge with corrugated steel webs is taken as the background. The difference between the precast segmental composite box girders with corrugated steel webs and the traditional concrete box girder is proven by numerical simulation. The stress and deformation characteristics of the segmental girder during storage and hoisting are analysed, and reasonable control measures are proposed. The data suggested that compared with ordinary concrete box girders, the smaller torsional stiffness and lateral stiffness of the precast segmental composite box girder with corrugated steel web segments lead to larger roof stress and deformation during the storage and hoisting periods. The number of storage layers of segmental girders should not exceed two, and the four hoisting point scheme should be adopted for hoisting. It is recommended to set one to two channel steel supports of no less than 20 grade steel between the top and bottom plates to avoid excessive deformation of the roof. With the increase in the segment length, the roof deformation and stress increased regardless of the storage period and the hoisting period. If the safety factor needs to be increased, when the segment length is short (1.6 m–3.2 m), increasing the support size is recommended. When the segment length is longer (4.0 m, 4.8 m), increasing the number of supports is recommended. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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13 pages, 6053 KiB

Open AccessArticle

Condition Assessment of Grouped Cable Forces of Cable-Stayed Bridge Using Deflection Data

by Xiaoling Liu, Xiyan Yi, Bing Wang and Ying Liu

Buildings 2023, 13(2), 472; https://doi.org/10.3390/buildings13020472 - 09 Feb 2023

Cited by 4 | Viewed by 1749

Abstract

The stress state of the cable group in a cable-stayed bridge directly affects the overall performance. A novel method for assessing grouped cable forces using deflection data is proposed in this article. Firstly, a simplified equation between the variation in cable forces and [...] Read more.

The stress state of the cable group in a cable-stayed bridge directly affects the overall performance. A novel method for assessing grouped cable forces using deflection data is proposed in this article. Firstly, a simplified equation between the variation in cable forces and the girder deflection was built according to the geometric relationship of the deformation. Secondly, the threshold value of cable force change rate for a single cable can be determined by the proposed theoretical equation and the deflection limit in the specification. On this basis, the evaluation standard of single cable force of piecewise linear mode was established. Thirdly, considering the uniform and non-uniform changes in the cable forces, the condition assessment method of grouped cable forces was established based on the variable weight synthesis method and the gray correlation degree theory. Finally, a case study of a real bridge was undertaken. The results show that the case data validate the correctness of the proposed theoretical equation. The threshold of change rate for long cable is 30%. Six-year assessment scores of grouped cables are generally decreasing, which also reflects the development of other component defects from the side. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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22 pages, 7858 KiB

Open AccessArticle

The Interfacial Friction Loss of Prestressed Carbon-Fiber Tendons in a Bending State

by Jiaping Fu, Tian Zeng, Bing Wang, Ping Zhuge, Jiajun Xia and Wanyun Cai

Buildings 2023, 13(1), 99; https://doi.org/10.3390/buildings13010099 - 30 Dec 2022

Cited by 2 | Viewed by 1599

Abstract

Carbon-fiber reinforced plastic (CFRP) is ideal for bridge reinforcement due to its high strength, light weight, and corrosion resistance. Studies on the friction loss of CFRP tendons in a bending state form an important part of advancing the application of CFRP materials to [...] Read more.

Carbon-fiber reinforced plastic (CFRP) is ideal for bridge reinforcement due to its high strength, light weight, and corrosion resistance. Studies on the friction loss of CFRP tendons in a bending state form an important part of advancing the application of CFRP materials to external prestressing strengthening technology. To understand the magnitude and variation of interfacial friction loss of prestressed CFRP tendons under bending conditions, 12 single-bending prestressing tension tests and 4 three-consecutive-bending prestressing tension tests were conducted in this study. Two bending radii of 1.5 m and 2 m, two bending angles of 20° and 30°, and three contact surfaces with different friction coefficients were selected for the steering block condition to measure the friction loss under each stage of tensioning prestress. On this basis, a model for calculating the friction loss rate on the surface of prestressed CFRP tendons was derived for the change of contact stress between CFRP tendons and deflectors during the installation and tensioning stages. The results show that the friction loss of external prestressed CFRP tendons is mainly related to four external factors: bending radius, steering angle, friction coefficient, and the magnitude of tensioning prestress; with the increase of prestress, the friction loss rate goes through three stages, the rising stage, the falling stage, and the stable stage; in the process of friction loss rate change, the main influencing factor controlling the magnitude of friction loss rate changes from bending radius to steering angle. In the theoretical calculation model of friction loss rate, the calculation model of the prestressed CFRP tendons under multiple successive bends can be simplified to a combination of several calculation models for a single bend. This study provides a reference for the engineering field of strengthening reinforced concrete (RC) beams using external prestressed CFRP tendons. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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19 pages, 3847 KiB

Open AccessArticle

Viscoelastic Solutions and Investigation for Creep Behavior of Composite Pipes under Sustained Compression

by Yinxia Yu, Wenqin Deng, Kong Yue and Peng Wu

Buildings 2023, 13(1), 61; https://doi.org/10.3390/buildings13010061 - 27 Dec 2022

Cited by 3 | Viewed by 1153

Abstract

Composite pipes, which are widely used for transporting fluids, have a high strength, good impermeability and strong resistance to external pressure. Because the pipe bears a sustained load, and its constituent materials usually possess time-dependent properties, the creep phenomenon unavoidably occurs in the [...] Read more.

Composite pipes, which are widely used for transporting fluids, have a high strength, good impermeability and strong resistance to external pressure. Because the pipe bears a sustained load, and its constituent materials usually possess time-dependent properties, the creep phenomenon unavoidably occurs in the composite pipes in the long run. The aim of this study is to propose analytical viscoelastic solutions, which are then applied to a composite pipe structure to explore the creep behavior of composite pipes under sustained compression. The pipe layers and the bonding interlayer both exhibit viscoelastic properties, which are the novelty of this study. The governing equations for the viscoelastic composite pipe are built on the basis of exact elasticity theory combined with the viscoelastic theory. General solutions are derived by means of a Fourier series expansion in which the coefficients are further determined by a Laplace transform. The research results indicate that the present solution has a higher computational efficiency than the finite element solution, because of the latter involving the time discretization method. In addition, for the viscoelastic pipe, if the modulus degradation of the neighboring laminar layers is proportional, the stresses can keep constant with time, as in a purely elastic material. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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22 pages, 10862 KiB

Open AccessArticle

Flexural Behavior of RC Beams with an Abrupt Change in Depth: Experimental Work

by Sabry Fayed, Emrah Madenci and Yasin Onuralp Özkılıç

Buildings 2022, 12(12), 2176; https://doi.org/10.3390/buildings12122176 - 08 Dec 2022

Cited by 4 | Viewed by 1751

Abstract

The most crucial components in the case of roofs with two levels or a variable floor height are variable depth beams. In order to investigate the flexural behavior of reinforced concrete (RC) beams with varying depths under static loads, experimental research was conducted. [...] Read more.

The most crucial components in the case of roofs with two levels or a variable floor height are variable depth beams. In order to investigate the flexural behavior of reinforced concrete (RC) beams with varying depths under static loads, experimental research was conducted. Under the four-point bending flexural test, two reference beams with constant depth, six dapped beams at the soffit, and four dapped beams at the top were tested. For all beams with a 150 mm depth, a 100 mm increase in depth occurred at the middle span of the beams. The primary characteristics included the impact of increasing depth, the impact of stirrups’ absence and their various ratios, and the characteristics of the longitudinal bars at the locations of sudden depth changes in either the top or bottom bars. Both the cracks’ progression and the load-deflection relationship along the beam’s length were observed. The ultimate carrying load (Pu) was reduced by 23.56% and 27.35% as a result of the 100 mm increase in the half-span of the beam over the constant depth in case of changes at the top and soffit, respectively. The Pu was increased by a ratio ranging from 20.9% to 31.35% for the bottom dapped beams and by a ratio of 29.79% for the top dapped beams due to the various stirrup ratios in the dapped area. The ductility was significantly impacted by the elevated stirrup ratios in the dapped area. The predicted results and the experimental results matched when the Pu of the tested beams was evaluated using the strut and tie model. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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17 pages, 3554 KiB

Open AccessArticle

UHPC-Filled Rectangular Steel Tubular Beam–Column: Numerical Study and Design

by Heng Cai and Yanxiang Yan

Buildings 2022, 12(11), 1882; https://doi.org/10.3390/buildings12111882 - 04 Nov 2022

Cited by 2 | Viewed by 1048

Abstract

This paper presents a numerical study on the nonlinear behaviors of UHPC-filled square steel tubular (UHPCFST) columns under complex actions. A novel fiber model was developed considering the local buckling effects of steel tubes. The reliability and robustness of the model were validated [...] Read more.

This paper presents a numerical study on the nonlinear behaviors of UHPC-filled square steel tubular (UHPCFST) columns under complex actions. A novel fiber model was developed considering the local buckling effects of steel tubes. The reliability and robustness of the model were validated by a large amount of experimental data in the reported literature. Then, the current design codes were evaluated and discussed on the basis of the collected experimental data, and a practical calculation method was finally proposed to predict the bending moment capacities of UHPCFST beam–columns. The results indicate that the proposed fiber model can accurately predict the nonlinear behaviors of UHPCFST beam–columns, including axial compression, eccentric compression, pure bending, and hysteretic behaviors. Compared with current design codes, the practical calculation method presents high precision and can accurately predict the bending moment capacities of UHPCFST beam–columns. Full article

(This article belongs to the Special Issue New and Future Progress for Concrete Structures)

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