Research

19 pages, 8270 KiB

Open AccessArticle

Seismic Performance and Nonlinear Strain Analysis of Mechanical Splices for High-Strength Reinforcement in Concrete Structures

by Hung-Jen Lee, Tzu-Yu Chang, Chien-Chung Chen and Ker-Chun Lin

Materials 2023, 16(12), 4444; https://doi.org/10.3390/ma16124444 - 17 Jun 2023

Viewed by 911

Abstract

This study investigates the strain development in reinforcing bars within the plastic hinge regions of beams and columns, with the main objective of modifying the current acceptance criteria for mechanical bar splices to accommodate high-strength reinforcement. The investigation utilizes numerical analysis based on [...] Read more.

This study investigates the strain development in reinforcing bars within the plastic hinge regions of beams and columns, with the main objective of modifying the current acceptance criteria for mechanical bar splices to accommodate high-strength reinforcement. The investigation utilizes numerical analysis based on moment–curvature and deformation analysis of typical beam and column sections in a special moment frame. The results indicate that the use of higher grade reinforcement, such as Grade 550 or 690, results in lower strain demands in the plastic hinge regions compared to Grade 420 reinforcement. To validate the modified seismic loading protocol, over 100 samples of mechanical coupling systems were tested in Taiwan. The test results demonstrate that the majority of these systems can successfully complete the modified seismic loading protocol and are suitable for use in critical plastic hinge regions of special moment frames. However, caution is advised for slender mortar-grouted coupling sleeves, as they were unable to fulfill the seismic loading protocols. These sleeves may be conditionally used in plastic hinge regions of precast columns, provided they meet specific conditions and demonstrate seismic performance through structural testing. The findings of this study offer valuable insight into the design and application of mechanical splices in high-strength reinforcement scenarios. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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22 pages, 8615 KiB

Open AccessArticle

Performance of Manufactured and Recycled Steel Fibres in Restraining Concrete Plastic Shrinkage Cracks

by Talal O. Alshammari, Kypros Pilakoutas and Maurizio Guadagnini

Materials 2023, 16(2), 713; https://doi.org/10.3390/ma16020713 - 11 Jan 2023

Cited by 3 | Viewed by 1503

Abstract

Early-age plastic shrinkage cracks can reduce the durability of concrete slabs by creating direct paths for the ingress of aggressive agents and thus accelerating degradation due to environmental attack, in particular, in hot and windy environments. The elimination of such cracks is essential [...] Read more.

Early-age plastic shrinkage cracks can reduce the durability of concrete slabs by creating direct paths for the ingress of aggressive agents and thus accelerating degradation due to environmental attack, in particular, in hot and windy environments. The elimination of such cracks is essential for durable and sustainable concrete structures. This paper parametrically investigates the effect of manufactured steel fibres (MSF) and recycled tyre steel fibres (RTSF) on restraining plastic shrinkage and micro cracks at different dosages (10, 20, and 30 kg/m³). The plastic shrinkage tests were carried out in a specially designed chamber, according to ASTM C1579. Various environmental conditions are examined, and their impact on compressive strength and crack potential is assessed. A digital image analysis technique is used to measure length, width, and the area of the crack on the exposed surface to gain additional insights into crack behaviour. The results show a slight early-age (one-day) increase in compressive strength for the concrete exposed to the various environmental conditions, mostly as a result of higher temperatures. Through the use of the crack reduction ratio (CRR), both RTSF and MSF are shown to be successful in controlling plastic shrinkage and micro cracks, with the RTSF being superior due to the fact that they are better distributed in the concrete volume. The addition of 30 kg/m³ of RTSF was effective in preventing crack development in most environments or restraining cracks in extremely harsh environments. The adoption of these results will lead to more sustainable concrete slabs in the harsher environmental conditions created by climate change. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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19 pages, 3485 KiB

Open AccessArticle

Optimization of Steel Roof Framing Taking into Account the Random Nature of Design Parameters

by Paweł Zabojszcza and Urszula Radoń

Materials 2022, 15(14), 5017; https://doi.org/10.3390/ma15145017 - 19 Jul 2022

Viewed by 1099

Abstract

The main subject of this paper is an optimization of steel roof framing used as a load-bearing structure in commercial pavilions. The authors wanted to draw attention to the necessity to take into account the uncertainty in the description of design parameters during [...] Read more.

The main subject of this paper is an optimization of steel roof framing used as a load-bearing structure in commercial pavilions. The authors wanted to draw attention to the necessity to take into account the uncertainty in the description of design parameters during optimization. In the first step, using geometrically nonlinear relationships, a static-strength analysis is performed. The decisive form of loss of stability in this steel roof framing is the jump of the node (snap-through), and not the buckling of the most stressed structure bars. Therefore, when creating the limit function, it was decided to make a condition limiting the permissible displacement. Values of the implicit limit function were calculated with Abaqus software based on the finite element method. Reliability analysis, and robust and deterministic optimization were performed using Numpress Explore software. Numpress Explore software communicates with the Abaqus software to perform analysis. The task ended with the generation of information that contained the failure probability, reliability index and the values of optimized areas of the bars’ cross-sections. The end result of the optimization is not a cost analysis, but an assessment of the safety of the structure. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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20 pages, 7909 KiB

Open AccessArticle

Effects of Concrete Grades and Column Spacings on the Optimal Design of Reinforced Concrete Buildings

by Mohammed Rady and Sameh Youssef Mahfouz

Materials 2022, 15(12), 4290; https://doi.org/10.3390/ma15124290 - 17 Jun 2022

Cited by 13 | Viewed by 2192

Abstract

This paper investigates the effects of concrete grades and column spacings on the optimal design of reinforced concrete (RC) buildings. To this end, cost design optimization was performed for buildings with three different floor systems: flat plates (FS), flat slabs with drop panels [...] Read more.

This paper investigates the effects of concrete grades and column spacings on the optimal design of reinforced concrete (RC) buildings. To this end, cost design optimization was performed for buildings with three different floor systems: flat plates (FS), flat slabs with drop panels (FSDP), and solid slabs (SS). The evolutionary method provided by the Excel solver was used as the optimization algorithm because it can deal with the complex nature of structural design problems. The objective function was the total construction cost of the building, including the costs of concrete, reinforcement bars, labor, and formwork, while still fulfilling the constraints of the Egyptian code of practice (ECP-18). The applicability of the presented algorithm was investigated in a design example, where the tuning of the evolutionary algorithm control parameters was sought, and the best parameters were investigated. Two case studies were employed to study the impacts of changing the column spacing and concrete grades on the optimal cost for each floor system. The results showed that low concrete grades, (i.e., characteristic strength up to 40 MPa) and column spacings up to 5 m are preferred in terms of direct construction costs for low-rise RC residential buildings. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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23 pages, 6112 KiB

Open AccessArticle

Seismic Retrofitting of Existing Industrial Steel Buildings: A Case-Study

by Roberto Tartaglia, Aldo Milone, Alessandro Prota and Raffaele Landolfo

Materials 2022, 15(9), 3276; https://doi.org/10.3390/ma15093276 - 03 May 2022

Cited by 13 | Viewed by 2008

Abstract

Industrial single-storey buildings are the most diffuse typology of steel construction located in Italy. Most of these existing buildings were erected prior to the enforcement of adequate seismic provisions; hence, crucial attention is paid nowadays to the design of low-impact retrofit interventions which [...] Read more.

Industrial single-storey buildings are the most diffuse typology of steel construction located in Italy. Most of these existing buildings were erected prior to the enforcement of adequate seismic provisions; hence, crucial attention is paid nowadays to the design of low-impact retrofit interventions which can restore a proper structural performance without interrupting productive activities. Within this framework, an existing industrial single-storey steel building located in Nusco (Italy) is selected in this paper as a case-study. The structure, which features moment resisting (MR) truss frames in both directions, is highly deformable and presents undersized MR bolted connections. Structural performance of the case-study was assessed by means of both global and local refined numerical analyses. As expected, the inadequate performance of connections, which fail due to brittle mechanisms, detrimentally affects the global response of the structure both in terms of lateral stiffness and resistance. This effect was accounted for in global analyses by means of properly calibrated non-linear links. Thus, both local and global retrofit interventions were designed and numerically investigated. Namely, lower chord connections were strengthened by means of rib stiffeners and additional rows of M20 10.9 bolts, whereas concentrically braced frames (CBFs) were placed on both directions’ facades. Designed interventions proved to be effective for the full structural retrofitting against both seismic and wind actions without limiting building accessibility. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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29 pages, 6865 KiB

Open AccessArticle

Optimal Design of Reinforced Concrete Materials in Construction

by Mohammed Rady, Sameh Youssef Mahfouz and Salah El-Din Fahmy Taher

Materials 2022, 15(7), 2625; https://doi.org/10.3390/ma15072625 - 02 Apr 2022

Cited by 14 | Viewed by 3248

Abstract

The structural design process is iterative and involves many design parameters. Thus, this paper presents a controlled framework for selecting the adequate structural floor system for reinforced concrete buildings and efficiently utilizing the corresponding construction materials. Optimization was performed using an evolutionary algorithm [...] Read more.

The structural design process is iterative and involves many design parameters. Thus, this paper presents a controlled framework for selecting the adequate structural floor system for reinforced concrete buildings and efficiently utilizing the corresponding construction materials. Optimization was performed using an evolutionary algorithm to minimize the total construction cost, considering the costs of concrete, steel reinforcement, formwork, and labor. In the problem formulation, the characteristic compressive strength of concrete was treated as a design variable because it affects the mechanical performance of concrete. The design variables included the column spacings, concrete dimensions, and steel reinforcement of different structural components. The constraints reflected the Egyptian code of practice provisions. Because the choice of the structural floor system affects the design details, three systems were considered: solid slabs, flat slabs with drop panels, and flat slabs without drop panels. Two benchmark examples were presented, and the optimal design results of the structural floor systems were compared. The solid slab system had the lowest construction cost among the three structural floor systems. Comparative diagrams were developed to investigate the distribution of construction costs of each floor system. The results revealed that an adequate choice of design variables could save up to 17% of the building’s total construction cost. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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26 pages, 9545 KiB

Open AccessArticle

The Effect of Steel Beam Elastic Restraint on the Critical Moment of Lateral Torsional Buckling

by Rafał Piotrowski and Andrzej Szychowski

Materials 2022, 15(4), 1275; https://doi.org/10.3390/ma15041275 - 09 Feb 2022

Cited by 4 | Viewed by 5101

Abstract

This paper reports the results of the next stage of the authors’ investigations into the effect of the elastic action of support nodes on the lateral torsional buckling of steel beams with a bisymmetric I-section. The analysis took into account beam elastic restraint [...] Read more.

This paper reports the results of the next stage of the authors’ investigations into the effect of the elastic action of support nodes on the lateral torsional buckling of steel beams with a bisymmetric I-section. The analysis took into account beam elastic restraint against warping and against rotation in the bending plane. Such beams are found in building frames or frame structures. Taking into account the support conditions mentioned above allows for more effective design of such elements, compared with the boundary conditions of fork support, commonly adopted by designers. The entire range of variation in node rigidity was considered in the study, namely from complete freedom of warping to complete restraint, and from complete freedom of rotation relative to the stronger axis of the cross section (free support) to complete blockage (full fixity). The beams were conservatively assumed to be freely supported against lateral rotation, i.e., rotation in the lateral torsional buckling plane. Calculations were performed for various values of the indexes of fixity against warping and against rotation in the beam bending plane. In the study, formulas for the critical moment of bilaterally fixed beams were developed. Also, approximate formulas were devised for elastic restraint in the support nodes. The formulas concerned the most frequent loading variants applied to single-span beams. The critical moments determined in the study were compared, with values obtained using LTBeamN software (FEM). Good compliance of results was observed. The derived formulas are useful for the engineering design of this type of structures. The designs are based on a more accurate calculation model, which, at the same time offers simplicity of calculation. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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18 pages, 6917 KiB

Open AccessArticle

Analysis of Failure Mechanism in Joints with Positive Eccentricity in CFS Truss

by Małgorzata Gordziej-Zagórowska, Elżbieta Urbańska-Galewska and Patryk Deniziak

Materials 2021, 14(22), 6986; https://doi.org/10.3390/ma14226986 - 18 Nov 2021

Viewed by 1564

Abstract

The paper presents studies concerning the load-bearing capacity of truss joints with a positive eccentricity resulting from the arrangement of geometric members and the failure mechanisms observed in the joints. Based on the previously conducted experimental study, a numerical model of the tested [...] Read more.

The paper presents studies concerning the load-bearing capacity of truss joints with a positive eccentricity resulting from the arrangement of geometric members and the failure mechanisms observed in the joints. Based on the previously conducted experimental study, a numerical model of the tested fragment of the CFS truss with eccentricity in the joint was created and validated. All structural details of the tested truss and the loading method consistent with the experiment were taken into account. The results obtained from a uniaxial tensile tests on a steel samples and results estimated during destructive tests carried out on a full-scale of research model were taken into account in validation of the numerical model. Next, appropriate numerical analyses were carried out and parameters such as the eccentricity size in the joint and the wall thickness of sections (t = 1.0, 1.5 and 4.0 mm) were modified. In the range of the studied wall slenderness from λ > 70 (1.0 mm and 1.5 mm thick), it was confirmed that the resistance of truss joints made from CFS open cross-sections with a positive eccentricity, is greater than the resistance that results from known methods of steel structure dimensioning. Full article

(This article belongs to the Special Issue Steels and Reinforced Concrete in Structural Engineering: Design and Applications)

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