• Computers and Concrete
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• v.19 no.4
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• pp.413-417
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• 2017

Concrete is a material popularly used in construction. Due to the load-bearing and external environmental factors during utilization or manufacturing, its surface is prone to flaws, such as crack and leak. To repair these superficial defects and ultimately and avoid the deterioration of the concrete's durability, numerous concrete surface protective coatings and crack repair products have been developed. Currently, studies are endeavoring to exploit the mineralization property of microbial strains for repairing concrete cracks be the repairing material for crack rehabilitation. This research aims to use bacteria, specifically B. pasteurii, in crack rehabilitation to enhance the flexural and compression strength of the repaired concrete. Serial tests at various bacterial concentrations and the same $Urea-CaCl_2$ medium concentration of 70% for crack rehabilitation were executed. The results prove that the higher the concentration of the bacterial broth, the greater the amount of calcium carbonate precipitate was induced, while using B. pasteurii broth was for crack rehabilitation. The flexural and compression strengths of the repaired concrete test samples were the greatest at 100% bacterial concentration. Compared to the control group (bacterial concentration of 0%), the flexural strength had increased by 32.58% for 1-mm crack samples and 51.01% for 2-mm crack samples, and the compression strength had increased by 28.58% and 23.85%, respectively. From the SEM and XRD test results, a greater quantity of rectangular and polygonal crystals was also found in samples with high bacterial concentrations. These tests all confirm that using bacteria in crack rehabilitation can increase the flexural and compression strength of the repaired concrete.

• Computers and Concrete
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• v.19 no.4
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• pp.365-374
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• 2017

With the continuous evolution of the numerical methods and the availability of advanced constitutive models, it became a common practice to use complex physical and geometrical nonlinear numerical analyses to estimate the structural behavior of reinforced concrete elements. Such simulations may yield the complete time history of the structural behavior, from the first moment the load is applied until the total collapse of the structure. However, the evolution of the cracking pattern in geometrical discontinuous zones of reinforced concrete elements and the associated failure modes are relatively complex phenomena and their numerical simulation is considerably challenging. The objective of the present paper is to assess the applicability of the Applied Element Method in simulating the development of distinct failure modes in reinforced concrete walls subjected to monotonic loading obtained in experimental tests. A pushover test was simulated numerically on three distinct RC shear walls, all presenting an opening that guarantee a geometrical discontinuity zone and, consequently, a relatively complex cracking pattern. The presence of different reinforcement solutions in each wall enables the assessment of the reliability of the computational model for distinct failure modes. Comparison with available experimental tests allows concluding on the advantages and the limitations of the Applied Element Method when used to estimate the behavior of reinforced concrete elements subjected to monotonic loading.

• Computers and Concrete
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• v.20 no.5
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• pp.605-616
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• 2017

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

• Computers and Concrete
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• v.20 no.5
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• pp.539-544
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• 2017

Shear walls have high stiffness and strength; however, they lack energy dissipation and repairability. In this study, an innovative slotted shear wall featuring vertical slots and steel energy dissipation connectors was developed. The ductility and energy dissipation of the shear wall were improved, while sufficient bearing capacity and structural stiffness were retained. Furthermore, the slotted shear wall does not support vertical forces, and thus it does not have to be arranged continuously along the height of the structure, leading to a much free arrangement of the shear wall. A frame-slotted shear wall structure that combines the conventional frame structure and the innovative shear wall was developed. To investigate the ductility and hysteretic behavior of the slotted shear wall, finite element models of two walls with different steel connectors were built, and pushover and quasi-static analyses were conducted. Numerical analysis results indicated that the deformability and energy dissipation were guaranteed only if the steel connectors yielded before plastic hinges in the wall limbs were formed. Finally, a modified D-value method was proposed to estimate the bearing capacity and stiffness of the slotted shear wall. In this method, the wall limbs are analogous to columns and the connectors are analogous to beams. Results obtained from the modified D-value method were compared with those obtained from the finite element analysis. It was found that the internal force and stiffness estimated with the modified D-value method agreed well with those obtained from the finite element analysis.

• Computers and Concrete
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• v.20 no.5
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• pp.545-553
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• 2017

A pounding tuned mass damper (PTMD) can be considered as a passive device, which combines the merits of a traditional tuned mass damper (TMD) and a collision damper. A recent analytical study by the authors demonstrated that the PTMD base on the energy dissipation during impact is able to achieve better control effectiveness over the traditional TMD. In this paper, a PTMD prototype is manufactured and applied for seismic response reduction to examine its efficacy. A series of shaking table tests is conducted in a three-story building frame model under single-dimensional and two-dimensional broadband earthquake excitations with different excitation intensities. The ability of the PTMD to reduce the structural responses is experimentally investigated. The results show that the traditional TMD is sensitive to input excitations, while the PTMD mostly has improved control performance over the TMD to remarkably reduce both the peak and root-mean-square (RMS) structural responses under single-dimensional earthquake excitation. Unlike the TMD, the PTMD is found to have the merit of maintaining a stable performance when subjected to different earthquake loadings. In addition, it is also indicated that the performance of the PTMD can be enhanced by adjusting the initial gap value, and the control effectiveness improves with the increasing excitation intensity. Under two-dimensional earthquake inputs, the PTMD controls remain outperform the TMD controls; however, the oscillation of the added mass is observed during the test, which may induce torsional vibration modes of the structure, and hence, result in poor control performance especially after a strong earthquake period.

• Computers and Concrete
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• v.20 no.5
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• pp.563-572
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• 2017

Ordinary reinforced concrete (RC) and prestressed concrete bridges are two popular and typical types of short- and medium-span bridges that accounts for the vast majority of all existing bridges. The cost of maintaining, repairing or replacing degraded existing RC bridges is immense. Detecting the abnormality of RC bridges at an early stage and taking the protective measures in advance are effective ways to improve maintenance practices and reduce the maintenance cost. This study proposes a systematic method from influence line (IL) identification to damage detection with applications to RC bridges. An IL identification method which integrates the cubic B-spline function with Tikhonov regularization is first proposed based on the vehicle information and the corresponding moving vehicle induced bridge response time history. Subsequently, IL change is defined as a damage index for bridge damage detection, and information fusion technique that synthesizes ILs of multiple locations/sensors is used to improve the efficiency and accuracy of damage localization. Finally, the feasibility of the proposed systematic method is verified through experimental tests on a three-span continuous RC beam. The comparison suggests that the identified ILs can well match with the baseline ILs, and it demonstrates that the proposed IL identification method has a high accuracy and a great potential in engineering applications. Results in this case indicate that deflection ILs are superior than strain ILs for damage detection of RC beams, and the performance of damage localization can be significantly improved with the information fusion of multiple ILs.

• Computers and Concrete
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• v.18 no.6
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• pp.1083-1096
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• 2016

Beam-column joints are recognized as the weak points of reinforcement concrete frames. The ductility of reinforced concrete (RC) frames during severe earthquakes can be measured through the dissipation of large energy in beam-column joint. Retrofitting and rehabilitating structures through proper methods, such as carbon fiber reinforced polymer (CFRP), are required to prevent casualties that result from the collapse of earthquake-damaged structures. The main challenge of this issue is identifying the effect of CFRP on the occurrence of failure in the joint of a cross section with normal ductility. The present study evaluates the retrofitting method for a normal ductile beam-column joint using CFRP under monotonic and cyclic loads. Thus, the finite element model of a cross section with normal ductility and made of RC is developed, and CFRP is used to retrofit the joints. This study considers three beam-column joints: one with partial CFRP wrapping, one with full CFRP wrapping, and one with normal ductility. The two cases with partial and full CFRP wrapping in the beam-column joints are used to determine the effect of retrofitting with CFRP wrapping sheets on the behavior of the beam-column joint confined by such sheets. All the models are subjected to monotonic and cyclic loading. The final capacity and hysteretic results of the dynamic analysis are investigated. A comparison of the dissipation energy graphs of the three connections shows significant enhancement in the models with partial and full CFRP wrapping. An analysis of the load-displacement curves indicates that the stiffness of the specimens is enhanced by CFRP sheets. However, the models with both partial and full CFRP wrapping exhibited no considerable improvement in terms of energy dissipation and stiffness.

• Computers and Concrete
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• v.18 no.6
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• pp.1153-1173
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• 2016

According to deformation data measured in some high concrete dams, for dam body deformation, there is a complex relationship with dam height and water head for different projects, instead of a simple monotonic relationship consistently. Meanwhile, settlement data of some large reservoirs exhibit a significant deformation of reservoir basin. As water conservancy project with high concrete dam and large storage capacity increase rapidly these decades, reservoir basin deformation problem has gradually gained engineers' attentions. In this paper, based on conventional analytical method, an improved analytical method for high concrete dam is proposed including the effect of reservoir basin deformation. Though establishing FEM models of two different scales covering reservoir basin and near dam area respectively, influence of reservoir basin on dam body is simulated. Then, forward and inverse analyses of concrete dam are separately conducted with conventional and proposed analytical methods. And the influence of reservoir basin deformation on dam working behavior is evaluated. The results of two typical projects demonstrate that reservoir basin deformation will affect dam deformation and stress to a certain extent. And for project with large and centralized water capacity ahead of dam site, the effect is more significant than those with a slim-type reservoir. As a result, influence of reservoir basin should be taken into consideration with conducting analysis of high concrete dam with large storage capacity.

• Computers and Concrete
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• v.21 no.4
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• pp.407-417
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• 2018

Concrete which is a composite material is one of the most important construction materials. Compressive strength is a commonly used parameter for the assessment of concrete quality. Accurate prediction of concrete compressive strength is an important issue. In this study, we utilized an experimental procedure for the assessment of concrete quality. Firstly, the concrete mix was prepared according to C 20 type concrete, and slump of fresh concrete was about 20 cm. After the placement of fresh concrete to formworks, compaction was achieved using a vibrating screed. After 28 day period, a total of 100 core samples having 75 mm diameter were extracted. On the core samples pulse velocity determination tests and compressive strength tests were performed. Besides, Windsor probe penetration tests and Schmidt hammer tests were also performed. After setting up the data set, twelve artificial intelligence (AI) models compared for predicting the concrete compressive strength. These models can be divided into three categories (i) Functions (i.e., Linear Regression, Simple Linear Regression, Multilayer Perceptron, Support Vector Regression), (ii) Lazy-Learning Algorithms (i.e., IBk Linear NN Search, KStar, Locally Weighted Learning) (iii) Tree-Based Learning Algorithms (i.e., Decision Stump, Model Trees Regression, Random Forest, Random Tree, Reduced Error Pruning Tree). Four evaluation processes, four validation implements (i.e., 10-fold cross validation, 5-fold cross validation, 10% split sample validation & 20% split sample validation) are used to examine the performance of predictive models. This study shows that machine learning regression techniques are promising tools for predicting compressive strength of concrete.

• Computers and Concrete
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• v.21 no.5
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• pp.525-530
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• 2018

As a nondestructive testing method, the Schmidt rebound hammer is widely used for structural health monitoring. During application, a Schmidt hammer hits the surface of a concrete mass. According to the principle of rebound, concrete strength depends on the hardness of the concrete energy surface. Study aims to identify the main variables affecting the results of Schmidt rebound hammer reading and consequently the results of structural health monitoring of concrete structures using adaptive neuro-fuzzy inference system (ANFIS). The ANFIS process for variable selection was applied for this purpose. This procedure comprises some methods that determine a subsection of the entire set of detailed factors, which present analytical capability. ANFIS was applied to complete a flexible search. Afterward, this method was applied to conclude how the five main factors (namely, age, silica fume, fine aggregate, coarse aggregate, and water) used in designing concrete mixture influence the Schmidt rebound hammer reading and consequently the structural health monitoring accuracy. Results show that water is considered the most significant parameter of the Schmidt rebound hammer reading. The details of this study are discussed thoroughly.