نشریه مهندسی سازه و ساخت
سال دهم شماره 5 (پیاپی 70، امرداد 1402)

This paper evaluates the "Response Modification", "Reduction due to ductility" and "Over-strength" factors for steel frames with "Linked Columns Frame" as dual systems. Since, LCF is a relatively modern lateral load resisting system, the necessity of a more comprehensive study is felt for performance evaluation of these frames under strong ground motions. In this regard, steel frames equipped with the linked column frame with 3, 5, 7, 9, and 11 stories are designed based on the Iranian earthquake design code (Standard No. 2800, 4th version) and implemented in Opensees software. Response modification factor (R factor) is calculated based on the result of incremental dynamic analysis (IDA), linear and nonlinear dynamic analysis under far-field earthquakes which have been presented in FEMA-P695. For a more accurate assessment, the shear and flexure performance of link beams is investigated in this study. The results show that R factors change in the height of steel frames with LCF. However, the mean values of the R factor do not necessarily increase or decrease as the number of stories increases. In most cases, R factors for LCFs with shear links are larger than the related result of steel frames containing flexural links. Also, the R factor does not need to consider more than 6.0 for regular LCFs with studied shear link beam.

Nowadays, given to the scarcity of Oil and Gas resources onshore, and the increasing demand for construction of facilities in coastal areas the use of deep foundations for providing stability for marine infrastructures, such as Oil and Gas Drilling Rigs and Wind turbines, has gained an increasing attraction. Interests in research of helical piles have been arisen due to the advantages of such foundations. Physical modelling is one of the most common method in practice for performance evaluation of deep foundations which provides with the researcher the capability of repeatability. In addition, it is chip and easy-to-execute method compared to the in-situ pile loading tests. Frustum confining vessel (FCV), is one of the most effective tool for physical modeling approach. FCV has a conical shape, which can convert the vertical applied pressure to the base of the vessel, to horizontal stress and to produce a stress distribution similar to the idealized linear stress distribution of soil in situ. Consequently, each base pressure corresponds to a specific embedment depth in real-world. In this study, a new FCV device with an optimized dimensions with the capability of testing model piles in saturated soil samples was constructed. To the best of the author’s knowledge, the newly constructed apparatus is the only FCV with this capability. After performance evaluation of the device, the load-displacement of a helical pile with one and three helices at different relative densities, both in wet and saturated sand, was evaluated. Results indicate that as the relative density increases the interlocking of the sand and helices increases which yields to an increase in the ultimate bearing capacity of pile. On the other hand, the bearing capacity reduces significantly in saturated sands. Also, increasing the number of helices significantly increases the bearing capacity of the helical pile.

Schools and buildings with educational uses are considered as important buildings in most of the design regulations due to their large population. According to the Iranian Earthquake Regulations, these buildings with any type of structural system, must be designed in such a way that they have at least a level of safety performance against severe earthquakes. Concrete schools in Kermanshah province have a significant frequency due to economic considerations, availability of materials and proper execution speed. Meanwhile, a special type of these schools has been executed with great frequency in most cities of Kermanshah province. On the other hand, in the study of educational spaces after the November 2017 Sarpol-e-Zahab earthquake in Kermanshah province, several cases of structural and non-structural damages have been observed in schools. For this reason, in this study, the seismic performance of this type of schools, under the influence of possible earthquakes, as well as their vulnerability are evaluated by nonlinear static analysis methods and increasing dynamic analysis (IDA). Then, by performing nonlinear static analysis, the envelope curve of the structure is extracted and important parameters such as ductility and the coefficient of behavior are calculated. Moreover, by performing the IDA for this type of schools, the failure curves subjected to various records in comparison with the increasing acceleration are presented and studied. The results show that the behavior and vulnerability of this structure are different according to the type of site and different records of near and far zones of the earthquake. Also, the structure of this school has an acceptable performance despite the irregularity in the plan.

Geopolymers are aluminosilicate materials that can be a suitable alternative to all types of concrete, because they help preserve the environment by removing pollutants such as CO2. The present study examines the mechanical characteristics and durability of slag-based geopolymer mortars (GGBFS) and its replacement with different percentages of kaolin in several molar amounts. Sodium hydroxide with a concentration of 4 and 8 M and sodium silicate have been used as activators. The mentioned basic materials have been examined alone and in combination with other components of the mixture. For this purpose, kaolin powder has been mixed with slag in the percentages of 50% and 75%, which, including non-combined mixtures, has made a total of 12 mixing designs. The studied properties included: compressive, bending and tensile strengths, percentage of water absorption and electrical resistance at the age of 28 days. The compressive strength of geopolymer samples at the ages of 7, 28 and 90 days was determined and the following results were obtained: The use of polymer in the 7 and 28 day compressive strength test in the BS8 design sample compared to the S4 control design improved the strength of the samples by 15% and 24%, respectively. In the tensile test of the SC50-4 mixing design sample (2.79 Mpa) compared to the control S4 design sample (2.63 Mpa), the strength of the sample improved by 6%. In the flexural strength test, no significant difference was observed between the S4 design sample and the BS8 design sample. In the final water absorption test, the samples of mixing designs containing kaolin powder next to slag had almost the same water absorption.

Reinforced concrete structures with moment resisting frames are one of the most widely used structural systems in the world. High ductility, acceptable strength, ease of implementation, and fewer architectural limitations compared to other structural systems are the positive features of reinforced concrete moment-resisting frames. Construction errors and the use of improper mixing designs for concrete materials are generally the causes of the poor performance of these structures. In the present study, an attempt has been made to investigate the effect of concrete additives on the performance of conventional concrete structures with fabrication errors in an experimental study. three one-third-scale experimental specimens were constructed using Steel Fibers (SF) and Air Entering Admixture (AEA) materials at the beam-column joints. The samples were subjected to cyclic quasi-static loading in the laboratory. Seismic parameters of stiffness, ductility, ultimate strength, and energy dissipation capacity were obtained and evaluated from the hysteresis diagrams of experimental tests. The experimental results showed that the use of steel and polypropylene additives enhances the seismic performance of concrete structures and improves the parameters of stiffness, ultimate strength, and energy dissipation capacity; However, they do cause a slight decline in ductility. It was also concluded that if there is a construction error in the structure, the use of steel fibers additives will provide better behavior than a reinforced concrete frame with conventional materials.

To make structures resistant to earthquakes, various systems are used, one of the most important of these systems is a steel Moment frame with a steel shear wall, which has been used as one the systems since the 1970s. Steel shear walls are usually made in two types, stiffened and unstiffened. The idea of corrugated steel shear walls was proposed as a replacement for stiffened shear walls. These plates have high buckling resistance due to their out-of-plane stiffness. This research investigated the seismic behavior and vulnerability of steel structures with horizontally and vertically corrugated steel shear walls using ABAQUS nonlinear analysis software. For this purpose, after validation of the modeling by controlling with an experimental study, 280-time history analyses were conducted. Then fragility curves were produced on 3 and 10-story structures.7- acceleration records of the far-Fault earthquakes and 7 acceleration records of the near-fault earthquakes were used to generate the fragility curves. The results showed the 3-story structure suffered damage at a lower acceleration compared to the 10-story structure. The structure was more fragile under near-fault rather than far-fault earthquakes. The highest percentage of damage reduction in the far-fault earthquakes compared to the near-fault occurred in the 10-story structure at the life safety performance level (LS). Further in trapezoidal samples, by changing the direction of placement of corrugation plates from horizontal to vertical, the probability of wall failure decreased at different PGA levels.

This paper investigated the effect of the stiffness of a light panel type with polystyrene core and lightweight concrete coating on the behavior of plain steel frames. An experimental study was performed on two large-scale specimens of one-story single-span. The behavior of panels and determine the effect of their stiffness, an in-plane infill-frame interaction frame, including a steel frame with isolated and non-isolated panels, were investigated. The specimens were tested under controlled displacement to investigate the in-plane infill-frame interaction of steel frames. Both isolated and non-isolated panels were tested under quasi-static cyclic loading. The results show that the proper behavior of this type of panel in isolated and non-isolated frames, the global stiffness of the frames and panels are reduced with a gentle slope, and brittle failure does not occur in the frames and panels. In the isolated specimens, the relative displacement (drift) of 1%, and the stiffness was 1.22 kN/mm. When the drift increased to 2.5%, the stiffness decreased to 0.88 kN/mm. In the non-isolated specimens, the drift of 1%, and the stiffness was 2.49 kN/mm. When the drift increased to 2.5%, the stiffness decreased to 0.89 kN/mm. The behavior of the non-isolated frame after loading is similar to the isolated frame because only the corners of the panel failed. A similar result was obtained in the failure pattern. In other words, the corners of the non-isolated panels attached to the frame failed by increasing the displacement due to in-plane infill-frame interaction. In the subsequent cycles, another part of the corners of the panels failed again. Complete failure was not observed in the panels. Similarly, in the non-isolated specimens, the panels remain without global failure after applying the cyclic load. The behavior of the non-isolated frame is similar to the isolated frame, with a decreased stiffness.

Investigation of the nonlinear behavior of SPSWs requires complex non-linear finite element analyses. These analyses have some drawbacks namely convergence problems, time-consuming, and the need for expertise. Therefore, it is necessary to propose a comprehensive method that can solve the problems of current methods. In this research, a novel approach based on the use of axial members to evaluate the nonlinear behavior of SPSWs with any arbitrary configuration is developed. The innovation of the proposed method is that the obstacles in modeling of shear walls with different shapes and aspect ratios have been solved. Moreover, due to the low computational cost of this method, i.e., a 60% reduction in modeling time, and a saving of 92% and 66% in analysis time in static and cyclic loading, respectively, full-scale structures can be analyzed with acceptable accuracy. In addition, owing to its comprehensiveness, this method can be placed in existing commercial software, or it is possible to be developed as software. To evaluate the efficiency of the proposed method, 4 different SPSWs with different mechanical and geometric characteristics were analyzed using the proposed method. The results showed a good agreement between the outputs of the proposed method and the actual behavior of the SPSW, which verifies the suitable performance of the method. The results of analysis using the proposed method indicated that the maximum shear stress ratio occurs at the lower H/L and thickness. In addition, increasing the thickness and H/L of the infill results in an increase in the shear that can be tolerated by the section as well as a reduction in the stress ratio. The average of reduction for an increase in thickness and H/L is 61.8% and 72 %, respectively.

The presence of holes in the sensitive areas of the beam-to-column connection can cause unwanted damage. In this article, using the connection truss model and time history loading, the effect of the mentioned holes in changing the functional levels of the connection has been investigated. Validation was done by modeling and numerical analysis of a healthy lateral connection whose cyclic test results are available up to the collapse threshold. Four functional levels were defined based on the crack width and the effect of the presence of the cavity on the change of the crack width in the connection was investigated. It was found that due to the creation of an air cavity, the bearing capacity of the connection is reduced and it enters the failure range earlier, but the presence of the cavity can change the way of damage distribution in the connection so that some cracks are more open and others are closed. Also, the sliding of rebars increases due to the presence of holes in compression cycles, these changes increase the need for connection ductility. So that in the recent study, this slip shows an increase of up to 91%. By dividing the connection into 40 equal parts and placing the hole in different parts, the holes created at the joint of beam and column can be more destructive. On the other hand, the sensitivity is less than the central cavities. Also, the holes placed in the vicinity of the longitudinal bars, even with a small volume, can accelerate the destruction of the connection due to the intensification of the slip. It was found that the presence of a cavity can increase energy consumption, so that a cavity with a volume of 2.5% near the column can improve the average amount of energy loss by 1.6%.

The present paper aimed to estimate the ground surface settlement induced by circular tunnel excavation in cohesive soils by considering the uncertainties of geometrical and geotechnical parameters. To this end, after numerical simulation of the tunnel based on the two-dimensional finite difference method in FLAC2D, the ground surface settlement profiles were analyzed using regression analysis (Gaussian equation). The effect of parametric changes of geometrical and geotechnical parameters on ground surface settlement has been studied based on dimensionless ratios including depth to tunnel diameter (C/D), soil strength (γD/Su) and soil stiffness (E/Su). The results showed that by increase in the C/D (increase of overburden pressure of the tunnel), the settlement increases. As γD/Su increases (soil weakening), the amount of settlement increases at a constant C/D and E/Su. The rate of change of settlement increase in γD/Su ratios occurs with more intensity than the increase in C/D. This indicates the greater impact of geotechnical parameters of the soil around the tunnel on surface settlement in comparison with geometric parameters. There is an inverse relationship between E/Su changes and surface settlement, and with increasing E/Su (soil stiffness), settlement decrease. Then, using the Gene Expression Programming (GEP) algorithm and forming a database containing of 1000 different simulations in terms of a combination of changes in C/D, γD/Su for constant E/Su (inputs) and Smax/H results (output), two new empirical equations were proposed as optimal empirical models for estimating the normalized ground surface settlement. The results of this study confirm that instead of measuring the time-consuming and complex conditions of ground surface settlement due to tunnel excavation on a real scale, soft calculations can be used to predict such features faster and more economically in tunnel excavation.

The phenomenon of damage in structures causes a change in the mass, stiffness and damping properties of the structure. As a result, the static and dynamic responses of the structure also change and therefore by using the responses of the structure, damage can be identified in the structure. In this article, a two-step method is introduced to identify the damage of structures under variable ambient temperature conditions. First, the principal components method has been used to extract the effect of ambient temperature from the obtained structural responses. In the first stage, various damage indices, which include the modal strain energy, frequency response function strain energy dissipation ratio and flexibility strain energy damage ratio, have been calculated. Then the Bayesian data fusion method has been applied to find the location of damage for these three indicators. The proposed method has significantly reduced the number of suspected damaged elements. In the second stage, the modal response of the structure is used and subsequently updated by multi-trial vector-based differential evolution to estimate the damage extents of the suspected elements. The results obtained from the analysis of two numerical examples show the high accuracy and fast convergence rate of the objective functions using the proposed method.

Modeling of elastic half-spaces and wave propagation within half-spaces under dynamic impulse loading has numerous applications namely designing of structures. In explosion topics with respect to the pursued purpose, multiple explosions can be replaced by one explosion. So this research deals with the effect of two explosions and determining the critical zones for various goals. This study deals with wave propagation in soil half-spaces considering on the ground structures. Structural analysis is the first step for designing structures. Therefore, the study of soil media responses under the surface structure is the goal of present research. The 3D elastic half-space with absorbing boundaries under two surface explosions is modeled using ANSYS finite element software. The surface responses are correlated to loading through a parametric study varying spatial distance and time delay of two similar blasts. Spatial distance and time delay are analysis parameters. Model responses determined in this study are: displacement, velocity and acceleration spectra (surface responses). In summary, surface responses show, peak of the double blast spectra occur in smaller periods than single blast, also by increasing spatial distance, peak of the double blast spectra occur in larger periods. Comparing spectra reveal second blast has minimum effect on surface spectra and maximum effect on acceleration spectra.