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21 pages, 8840 KiB

Open AccessArticle

Study on Mechanical Properties of Steel Fiber-Reinforced Geopolymer Concrete under Multi-Axial Loads

by Pengtao Wu, Xuan Wan, Qun Lu and Yan Zhang

Buildings 2024, 14(9), 2780; https://doi.org/10.3390/buildings14092780 - 4 Sep 2024

Viewed by 635

Steel fiber-reinforced geopolymer concrete (SFRGPC) is an inorganic cementitious material with environmentally friendly features. As compared to conventional concrete, SFRGPC has greater strength and durability, but it is brittle, making it similar to ordinary concrete. To date, the triaxial mechanical properties that regulate [...] Read more.

Steel fiber-reinforced geopolymer concrete (SFRGPC) is an inorganic cementitious material with environmentally friendly features. As compared to conventional concrete, SFRGPC has greater strength and durability, but it is brittle, making it similar to ordinary concrete. To date, the triaxial mechanical properties that regulate SFRGPC’s structural performance at serviceable and ultimate-limit conditions remain poorly understood. In this study, we conducted experimental and theoretical analyses of these properties. Conventional triaxial testing is used to investigate the effects of varying steel fiber contents and ratio of length to diameter under different confinement pressures on SFRGPC’s mechanical properties. The failure mode, maximal strength, stress–strain curve, maximum strain, and compressive toughness were analyzed and discussed. Under uniaxial compression, the failure mode of the SFRGPC specimens was a longitudinal split failure. The brittleness of the SFRGPC can be eliminated, and its resistance to breaking can be greatly improved by increasing the volume of steel fibers and the confining pressure in the mixture. The steel fiber content and ratio of length to diameter have obvious influence on the compressive strength of SFRGPC. As the steel fiber content increased, the compressive strength increased by 1.15–1.44 times; as the ratio of length to diameter increased, the compressive strength increased by 1.21–1.70 times. The increase in confining pressure can improve the compressive strength of concrete. With the increase in confining pressure, the increase trend of compressive strength becomes smooth. The confining pressure, steel fiber content, and steel fiber length have substantial influences on the compressive toughness index

η_{c 3}

. Under increasing confining pressure,

η_{c 3}

increases linearly; however, after confining pressure is higher than 5 MPa,

η_{c 3}

tends toward a steady state when the confining pressure increases. Using numerical simulation, we also investigated the size effect of SFRGPC under triaxial load. The concrete cylinder’s strength does not significantly decrease as its size increases. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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26 pages, 10124 KiB

Open AccessArticle

Study on Seismic Behavior of Different Forms of Eccentrically Braced Steel Frames

by Bo Liu, Yankai Lu, Weitao Li, Jiayue Li, Jingchen Zhao, Shuhe Wang, Guowei Ni and Qingjuan Meng

Buildings 2024, 14(7), 2064; https://doi.org/10.3390/buildings14072064 - 5 Jul 2024

Viewed by 710

Abstract

The arrangement of eccentric bracing has a significant impact on the seismic performance of structures. However, there is no further stipulation on different forms of eccentric bracing in the current Chinese code. At the same time, there is a lack of research on [...] Read more.

The arrangement of eccentric bracing has a significant impact on the seismic performance of structures. However, there is no further stipulation on different forms of eccentric bracing in the current Chinese code. At the same time, there is a lack of research on the seismic loss of eccentrically braced structures by Chinese domestic scholars. Therefore, this paper designs different forms of eccentrically braced frames and analyzes them according to the concept of seismic engineering based on performance, which provides some reference for the selection of the eccentrically braced steel frame structure layout in future engineering practice. In this paper, K-shaped, V-shaped, and D-shaped eccentrically braced steel frame structures with 3, 5, and 8 floors are designed, and the finite element analysis model is used for static napping and dynamic time history analysis. The results show that the K-shaped eccentrically braced structure has the best performance in bearing capacity and stiffness and has good seismic and collapse resistance performance. In the FEMA P-58 seismic assessment and vulnerability assessment, it is found that the V-shaped eccentrically braced structure has the smallest loss. However, it is necessary to fully consider the acceleration sensitivity of the non-structural components in the design. In general, the seismic performance of the eccentrically braced structure is improved by the energy dissipation beam yielding to consume energy, which provides a useful reference for structural design. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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21 pages, 3932 KiB

Open AccessArticle

Study on the Vibration Isolation Performance of Sliding–Rolling Friction Composite Vibration Isolation Bearing

by Yankai Lu, Jiayue Li, Bo Liu, Juannong Chen, Wanying Zhang and Qingjuan Meng

Buildings 2024, 14(7), 2053; https://doi.org/10.3390/buildings14072053 - 5 Jul 2024

Viewed by 694

Abstract

This study focuses on investigating the newly proposed sliding–rolling friction composite seismic isolation bearing. It begins by establishing the dynamic equilibrium equation for the structure. Subsequently, this paper proposes a calculation model for the sliding–rolling friction composite seismic isolation bearing, integrating fundamental theories [...] Read more.

This study focuses on investigating the newly proposed sliding–rolling friction composite seismic isolation bearing. It begins by establishing the dynamic equilibrium equation for the structure. Subsequently, this paper proposes a calculation model for the sliding–rolling friction composite seismic isolation bearing, integrating fundamental theories of structural dynamic response analysis and numerical solution methods. Utilizing finite element analysis software ABAQUS (2021), the mechanical properties of the seismic isolation bearing are comprehensively assessed. Through this evaluation, the optimal parameters of the seismic isolation bearing are determined. The findings reveal that the optimal parameters include a friction coefficient (μ) of 0.04, four U-type dampers at 45° angles, a width of 60 mm, five balls, and two shims. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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13 pages, 2740 KiB

Open AccessArticle

Time-Dependent Behavior of Ultra-High Performance Concrete Beams under Long-Term Bending Loads

by Jiayue Li, Yankai Lu, Xiaorui Jia, Bo Liu, Juannong Chen and Qingjuan Meng

Buildings 2024, 14(6), 1761; https://doi.org/10.3390/buildings14061761 - 11 Jun 2024

Viewed by 814

Abstract

In the past, scholars have studied the creep of UHPC, mainly in compression and tension but not bending creep. In this research, 20 ultra-high performance concrete (UHPC) beams were tested for bending creep under long-term loading, and the changes of beam deflection, temperature, [...] Read more.

In the past, scholars have studied the creep of UHPC, mainly in compression and tension but not bending creep. In this research, 20 ultra-high performance concrete (UHPC) beams were tested for bending creep under long-term loading, and the changes of beam deflection, temperature, and humidity with time were obtained for 445 days of continuous loading. The deflection patterns of UHPC beams with time were analyzed for different steel fiber content, curing systems, water/binder ratio, sand/binder ratio, and stress levels. The results showed that steel fiber had an obvious inhibition effect on initial deflection, but a dosage of steel fiber too high would offset part of the inhibition effect of steel fiber on creep. The use of heat treatment had a better inhibition of creep in the later stage of UHPC, but heat treatment must be matched with necessary moisture content, and hot water maintenance was the most efficient. Both a high water/binder ratio and high stress level increased the bending creep of the specimen. Bending creep increased with the increase in the sand/binder ratio. Therefore, attention should be paid to the total amount and ratio of cementitious materials and fine aggregates in UHPC. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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11 pages, 2629 KiB

Open AccessArticle

Clinker-Free Cement Manufactured with Metallurgical Slags

by Marcel Demarco, Fernando Vernilli and Sara Carvalho Zago

Buildings 2024, 14(6), 1739; https://doi.org/10.3390/buildings14061739 - 10 Jun 2024

Cited by 1 | Viewed by 909

Abstract

Steel slag is a significant environmental liability generated by pyrometallurgical processes. Residue generation, such as granulated blast furnace slag and basic oxygen slag (BOF), is intrinsic in steel production. Blast furnace slag, generated in the carbothermal reduction of iron ore, is almost entirely [...] Read more.

Steel slag is a significant environmental liability generated by pyrometallurgical processes. Residue generation, such as granulated blast furnace slag and basic oxygen slag (BOF), is intrinsic in steel production. Blast furnace slag, generated in the carbothermal reduction of iron ore, is almost entirely used as a supplementary cement material in Portland cement. BOF slag, produced in the conversion of pig iron into steel in a basic oxygen converter, is still not consolidated or valued for reuse. This research proposes the reuse and valorization of BOF slag combined with blast furnace slag in clinker-free cement production. Cement formulations were produced with different slag and gypsum contents, ranging from 80 to 90% blast furnace slag, 10 to 20% gypsum, and 10 to 15% BOF slag. All formulations were evaluated for compressive strength at ages of 3, 7, 14, 28, 91, and 180 days of curing. At the initial ages, the cement formulations exhibited high resistance. On the 3rd day, the cement formulations reached up to 10 MPa, and on the 7th day, 40 MPa. At late ages, the best-performing formulation, ECO2, showed, after 28 days of hydration, a compressive strength greater than 50 MPa, and at 180 days, a compressive strength greater than 80 MPa. It was possible to understand that BOF slag acts in cement alkaline activation with pH increase, more or less actively due to the presence of lime, portlandite, and calcite. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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13 pages, 1897 KiB

Open AccessArticle

New Natural Frequency Studies of Orthotropic Plates by Adopting a Two-Dimensional Modified Fourier Series Method

by Zhaoying Wu, An Li, Yu Wu, Zhiming Yin and Salamat Ullah

Buildings 2024, 14(3), 687; https://doi.org/10.3390/buildings14030687 - 5 Mar 2024

Cited by 1 | Viewed by 961

Abstract

The free vibration behavior of orthotropic thin plates, which are clamped at three edges and free at one edge, is a matter of great concern in the engineering field. Various numerical/approximate approaches have been proposed for the present problem; however, lack precise analytic [...] Read more.

The free vibration behavior of orthotropic thin plates, which are clamped at three edges and free at one edge, is a matter of great concern in the engineering field. Various numerical/approximate approaches have been proposed for the present problem; however, lack precise analytic benchmark solutions are lacking in the literature. In the present study, we propose a modified two-dimensional Fourier series method to effectively handle free vibration problems of plates under various edge conditions. In the given solution, the adopted trial function automatically satisfies several boundary conditions. After imposing Stoke’s transformation in the trial function and letting it satisfy the remaining boundary conditions, we can change the present plate problem into calculating several systems of linear algebra equations which are easily handled. The present method can be regarded as an easily implemented, rational, and rigorous approach, as it can exactly satisfy both the governing equation and the associated edge conditions. Another advantage of the present method over other analytical approaches is that it has general applicability to various boundary conditions through the utilization of different types of Fourier series, and it can be extended for the further dynamic/static analysis of plates under different shear deformation theories. Finally, all the novel analytical solutions are confirmed to be sufficiently accurate since they match well with the FEM results. The new analytic solution obtained may serve as a benchmark for validating other numerical and approximate methods. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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20 pages, 6750 KiB

Open AccessArticle

Enhancing Volumetric Stability of Metakaolin-Based Geopolymer Composites with Organic Modifiers WER and SCA

by Mo Zhang, Yongquan Zang and Lingyan Shan

Buildings 2024, 14(3), 586; https://doi.org/10.3390/buildings14030586 - 22 Feb 2024

Cited by 1 | Viewed by 1024

Abstract

Shrinkage during hardening and curing is one of the largest challenges for the widespread application of metakaolin-based geopolymers (MKGs). To solve this problem, a silane coupling agent (SCA) and waterborne epoxy resin (WER) were used to synthesize MKG composites. The individual and synergistic [...] Read more.

Shrinkage during hardening and curing is one of the largest challenges for the widespread application of metakaolin-based geopolymers (MKGs). To solve this problem, a silane coupling agent (SCA) and waterborne epoxy resin (WER) were used to synthesize MKG composites. The individual and synergistic effects of the SCA and WER on chemical, autogenous, and drying shrinkage were assessed, the modification mechanisms were investigated by microstructural characterization, and shrinkage resistance was evaluated by the chloride ion permeability of MKG composite coatings. The results showed that the SCA and WER significantly decreased the chemical shrinkage, autogenous shrinkage, and drying shrinkage of the MKG, with the highest reductions of 46.4%, 131.2%, and 25.2% obtained by the combination of 20 wt% WER and 1 wt% SCA. The incorporation of the organic modifiers densified the microstructure. Compared with the MKG, the total volume of mesopores and macropores in MKG-WER, MKG-SCA, and MKG-WER-SCA decreased by 11.5%, 8.7%, and 3.8%, respectively. In particular, the silanol hydrolyzed from the SCA can react with the opened epoxy ring of the WER and the aluminosilicate oligomers simultaneously to form a compact network and resist shrinkage during the hardening and continuous reaction of the geopolymer. Furthermore, the apparently lowered chloride ion diffusion coefficient of concrete (i.e., reduction of 51.4% to 59.5%) by the WER- and SCA-modified MKG coatings verified their improved shrinkage resistance. The findings in this study provide promising methods to essentially solve the shrinkage problem of MKGs at the microscale and shed light on the modification mechanism by WERs and SCAs, and they also suggest the applicability of MKG composites in protective coatings for marine concrete. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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21 pages, 5277 KiB

Open AccessArticle

The Generation of the Target Aftershock Spectrum Based on the Conditional Mean Spectrum of Aftershocks

by Ruiguang Zhu, Bohan Du, Yekai Yang and Dagang Lu

Buildings 2023, 13(10), 2660; https://doi.org/10.3390/buildings13102660 - 22 Oct 2023

Cited by 1 | Viewed by 1284

Abstract

Numerous studies have examined the responses of various structures to the mainshock–aftershock (MS–AS) ground motion, and the MS–AS ground motions are very important as the input. Therefore, in the absence of aftershock information, it is particularly critical to construct a reasonable MS–AS seismic [...] Read more.

Numerous studies have examined the responses of various structures to the mainshock–aftershock (MS–AS) ground motion, and the MS–AS ground motions are very important as the input. Therefore, in the absence of aftershock information, it is particularly critical to construct a reasonable MS–AS seismic sequence. This paper aims to provide a new reasonable method for generating the target aftershock response spectrum, which can be used to select or artificially simulate aftershock ground motion, given the seismic information of the main shock. Firstly, the magnitude, fault size, and location of the aftershock are determined. Then, other parameters required for the aftershock ground motion prediction equation (GMPE) are calculated. Subsequently, the correlation of the spectral shape to the MS–AS ground motion is used to modify the response spectrum predicted using the GMPE to obtain the conditional mean spectrum of aftershocks (CMS_A). Finally, the relative errors of the predicted spectrum via the ASK14 model and CMS_A are compared for four different assumptions. The results show that the simulated aftershock parameters and the actual ones accord well, and the relative errors of the CMS_A can be controlled within 20%. Meanwhile, the discrete property of the target aftershock response spectrum is closer to the real recorded response spectrum. Full article

(This article belongs to the Special Issue High-Performance Concrete: Modification Methods, Sustainability, and Multifunctional Applications)

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