JOURNAL OF STRUCTURAL AND CONSTRUCTION ENGINEERING
Year:2021 | Volume:8 | Issue:2|Papers Count:18

The earthquake is one of the natural hazards that have caused many casualties and financial losses throughout the world over the years. This has been the reason why the earthquake hazard analysis studies should be studied more seriously. Iran is also located in one of the seismically active regions of the world, the Himalayan-Alpine belt, which experiences many earthquakes every year. The Arias intensity function, as one of the important earthquake strong motion parameters, contributes greatly to the analysis of seismic hazard, which can be used to estimate the stability of slopes during the earthquake. The purpose of this research is to develop a new attenuation relationship for Arias intensity function in the Iranian plateau using intelligent methods. In this research, 1012 strong motion data were used. Initially, the data required to be filtered were corrected and then all data was analyzed. In this study, parameters such as magnitude of earthquake, focal depth, shear wave velocity and geographic position of the region were used as a variable for the attenuation relationship. Moment magnitude (Mw) was used as earthquake magnitude and earthquakes with magnitudes of above 4 were used in this research. The geographic location of Iran was divided into two regions of Central Alborz and the Zagros region. Gene Expression Programming (GEP), a kind of intelligent algorithm, was used as a method for regression and calculation of the objective function. The advantage of this method is that at first the model for the objective function is not specified and the model is presented optimally by the intelligent method. The fitness function is also defined based on the root least squared error (RMSE). Finally, the attenuation relation based on this fitness function was calculated and the observed results have a high fitness.

Reinforced concrete is the most commonly used construction material. The durability of reinforced concrete mostly depends on the surrounding environmental and exposure conditions such as carbonation, corrosion, and freezing and thawing. Corrosion of steel in concrete is one of the major causes of premature deterioration of reinforced concrete structures, leading to structural failure and is largely controlled by the permeability of the concrete cover to protect the steel reinforcement from corrosion. Therefore, the effect of silica fume, fly ash and zeolite pozzolans on the compressive strength, permeability and reinforcement corrosion is evaluated in this investigation. The compressive strength of 7 and 28-day concrete samples results show that silica fume results in compressive strength increase with respect to the control sample (without any pozzolans). Except for the samples containing zeolite with replacement weight percentages equal to 5, 10 and 15 percentage and fly ash with replacement weight percentage equal to 5 percentage, in other cases the compressive strength of 28-day samples containing fly ash and zeolite are lower than that of the control sample. The results of cylindrical chamber test also represent the permeability reduction of the 7-day samples containing these pozzolans with respect to the control sample. Based on the half-cell method test results, it is also observed that the resistance to corrosion of reinforcement concrete containing silica fume and zeolite is improved by using these pozzolans.

One of the important issues after an earthquake occurrence is to transfer residents to temporary accommodations. These points are areas of the city that have a higher safety factor against earthquake reoccurrence and have good access to management and relief centers. Due to the critical condition in the area after the earthquake, with the transfer of the township to these areas, relief procedure can be achieved with the highest speed and minimum risk. The purpose of this study is to determine the suitable locations for the construction of temporary accommodation facilities for injured people after earthquake occurrence in Karaj. To this end, firstly, the main controlling parameters in selection of the appropriate places for temporary accommodation are determined, and are classified into two groups of the main criteria of compatibility and incompatibility. The total number of the sub-criteria are twelve. Due to the spatial nature of this problem, fuzzy logic system with multi-criteria decision-making method is used to determine the most suitable points. After fuzzification of the criteria, their participation weight is determined and then, they are prioritized using fuzzy hierarchical analysis method. In the next step, desirability map of the region is prepared for each of the criteria. Eventually, by combining the impact of the studied criteria, a descriptive map of the region relative to the points of interest for temporary accommodation is generated. Based on this map, seven points are selected as suitable points for the construction of a temporary accommodation camp, and by employing the analytical hierarchy procedure with Expert Choice software, the optimal point is chosen.

A new kind of double skin CFT has more benefits in construction of bridge and especial buildings due to easily multi beam connections for central columns. In this study 27 double skin specimens filled with concrete, consist of internal circular tube and external hexagonal tubes have been studied using ABAQUSE finite element software. The effects of some parameters on behavior of CFT consists of: height of column, width to thickness ratio of external steel tube, diameter to thickness of internal tube and eccentricity were considered. Loading was applied as an axially compression in a displacement control state. The results show that whenever the eccentricity is matched through gap of two skins, the concrete confinement does not reduce, which is not the same as some codes of practice recommendations. The increase on strength of column depends on height, eccentricity and width to thickness ratio of external tube. The strength reduction of columns is up to 15% when height increases 50%. When the diameter to thickness, eccentricity and height of specimens remain constant, it was considered through the results that, the effects of width to thickness ratio of models is more significant than other parameters. The results also show that, when the height is constant and the width to thickness of external tube increases some outward foldings on columns were existe.

In this research, efforts were made to study the effects of water to cement ratio (W/C) and steel fibre volume fraction (V_f (%)) on the fracture parameters of self-compacting steel fibre-reinforced concrete using both Work Fracture and Size Effect Methods. In an experimental program, a variety of water to cement ratio and volume of steel fibres were considered and five mix designs were prepared in two series. In the first, water to cement ratio were altered (Includes values: W/C=0. 42, 0. 52, and 0. 62) with a constant volume of steel fibre (V_f=0. 3%), and in the second, varied volume of steel fibres (Includes values: V_f=0. 1, 0. 3, and 0. 5%) with a constant water to cement ratio (0. 52) were considered. Results have shown that an increase in the water to cement ratio reduces the fracture energy, However, we see a different behaviour in the lower water to cement ratio, while an increase in the volume of steel fibre not only increases the fracture energy causing the concrete to become more ductile, but it can also reduce the size effect greatly. G_F⁄ G_f has been found for all mix designs about 11. 81 and it has been concluded that the work fracture method yields more fracture energy than the Size effect method.

Severe damages of structures during large earthquakes and the loss of national wealth has made it extremely important to reduce the vibrations of structures against wind and earthquake. One of the efficient ways to reduce these vibrations, is to use the tuned liquid damper (TLD). The tuned liquid damper is the passive control system of the structure, which is made up of several fluid-containing reservoirs placed at the highest point of the building. The vibrational energy entangled to the structure is dissipated due to the turbulence of the liquid inside tanks. This system is used to control the vibrations of structures that have one or more degrees of freedom. In this research, the modified passive structural control system is used for checking the effects of the volumetric tuned liquid damper out and its results are compared with the traditional one. In this regard, three buildings including 4, 8 and 20 story moment resisting frames with three different mass ratio of 1, 2 and 3 percent were designed in ETABS software. Finally, Pushover analysis and nonlinear time history analyses were conducted in OPENSEES software results of the analysis show that the use of these dampers greatly reduces the peak drifts and peak residual drift demands of structures. On the other hand, the ability of the modified tuned liquid damper (MTLD) to reduce the residual and inter-story drift is greater in comparison to TLD.

The use of porous concrete system in urban areas as a modern and applied management approach during rainfall can prevent the problems by rapid outflow of the surface runoff. In this research, effect of replacing dolomite minerals in two modes of fine-grained and powder, as part of the aggregates or part of the cement, respectively, is investigated on the structural properties of porous concrete. In order to use porous concrete in urban runoff management system, the compressive strength and porosity should be considered. Two series of samples were made for structural experiments. The 15×15×15 cm samples were designed to test the compressive strength and the 10×10×10 cm samples were made to determine the porosity percentage. Statistical analyses of the laboratory results were performed using SPSS software. According to the results, replacement of dolomite powder for cement did not have significant effect on compressive strength and porosity. On the other hand, fine-grained dolomite has greatly improved the compressive strength. In addition to increasing the compressive strength, the porosity was increased due to the mechanism of particle placement in samples receiving 10% fine aggregates. Also adding 30% fine grained, increased compressive strength by 162%. This is while the porosity percentage has fallen sharply.

In the present study, the use of buckling-restrained braces (BRBs) has been evaluated as a research innovation aimed at reducing the potential of progressive collapse in steel braced frames. These braces prevent the overall buckling of brace and provide much more energy absorption than conventional convertible bracing systems. For this purpose, threedimensional finite element models of 4, 8, and 12-story buildings were simulated in two modes using ordinary and buckling braces and their response against progressive collapse was evaluated. The progressive collapse analysis was carried out using an alternative load path method and the response of the structures to column removal was investigated. Simulation of models was done using ABAQUS software. Also, the accuracy of the finite element method used in simulating the models was evaluated and a suitable agreement between the results was observed. The most significant results show that in steel frames that have BRBs, less stresses have been created compared with conventional steel braces. In all cases, BRBs with internal energy absorption of the structure have caused lower stresses to other structure member, thereby reducing the potential of progressive collapse. Also, the use of BRBs has reduced the rotation of the beam to column connection, compared to conventional bracing. This effect is especially noticeable in buildings with higher altitudes; the maximum amount of joint rotation corresponding to the 12-story building with BRBs has been reduced by 21% compared with the conventional braces. The reason for this is that, in buckling-restrained braces, the members are able to withstand a pressure above the tensile yield strength, and, unlike ordinary systems, the inherent ductility is due to the occurrence of yield in pressure before it begins to buckle.

The need to use non-uniform members in the structures from the past till now had been proposed although the subjects and research references in this case are insufficient. Therefore the use of non-uniform members is inevitable and should be carefully examined. About this members the main subject that should be investigated is buckling that if it occures it leads to member failure which may leads to collapse of the local or entire structure. So the exact solution of buckling load of non-uniform columns is available only for simple cases. In this paper a method based on finite element method is used for studing the problem of elastic buckling load of non-uniform columns with general cases of cross-section and axial loading. In first the column is devided to arbitrary numbers of finite elements. Then the stiffness matrix and geometric stiffness matrix is obtained based on existing relationship for each element and then for overall column. After applying boundary conditions using the eigenvalue equation to obtain the critical buckling load. It is clear that the effects of changes in cross-section of a column appear in stiffness matrix and changes in axial loading in geometric stiffness matrix. The proposed method in addition to high accuracy is general and could be used by the help of Matlab codes. Results obtained from this method are compared to ones that presented by Serna et al. The procedure in this paper is rating as a exact solutions but Serna’ s method is a closed form method that is from approximated solutions. The results are presented for uniform columns under non-uniform axial loading and non-uniform columns under non-uniform axial loading. Different non-uniform columns contain single web-tapered columns, double web-tapered columns and web-tapered & flange-tapered columns. Also results are presented for various end boundary conditions that contain hinged-hinged, clamped-clamped, hinged-clamped and clamped-free.

One of the factors of damage and destruction of concrete structures is fire. Concrete structures, in addition to having the proper mechanical characteristics, they must have durability properties to use their capacity over their lifetime. In this study, the effect of various volume fraction of steel fibers on improving the mechanical and durability properties of concrete at various temperatures has been investigated. Mechanical properties including compressive and tensile strength of concrete in the hot condition and the durability characteristics of the concrete after cooling, including surface water absorption, the penetration depth of water, electrical resistance and weight loss have been investigated. This study covers 0. 25 and 0. 50% volume fraction of steel fibers and temperatures of 28 to 800 ° C. The results show that the increase in compressive strength and tensile strength due to the age of the samples was higher in fiber concrete than non-fibrous concrete. It was also observed that the addition of 0. 25 and 0. 5% of steel fibers at the tested temperatures improved the compressive and tensile strength in the range of 10 to 27% and 8 to 200%, respectively. In addition, application of these fibers has reduced the sorptivity coefficient, the penetration depth of water, the electrical resistance of concrete and the weight loss of concrete owing to the high temperature. The results of this study showed that, at temperatures below 500 ° C specimens containing 0. 25% of steel fiber and 500 ° C onwards, specimens containing 0. 50% of steel fiber had the best performance on the improvement of the mechanical and durability properties of normal concrete at high temperatures.

Production of Portland Cement (PC) is a highly energy-intensive process and causes significant environmental damages. Thus scientists are always after ways to reduce these negative effects and find a more efficient process of producing cement. Geopolymers are amongst materials that are used as a substitute for cement in concrete. Geopolymer consists of one or more source materials containing alumino-silicate with an alkali activator. This study is done for the purpose of evaluating the setting time and compressive strength of geopolymer paste containing blast furnace slag and zeolite. Hence the setting time of geopolymer paste based on blast furnace slag and zeolite activated with sodium hydroxide solution of concentrations 6, 8, 10 and 12 molar and sodium silicate modulus of 2 was measured. In the next step, compressive strength of geopolymer paste samples under curing were gauged in the lab ambient temperature and also in the 60° C temperature. Results showed that with an increase in sodium hydroxide concentration, the setting time increased. Also compressive strength of geopolymer paste containing slag and zeolite rose with the raise of sodium hydroxide concentration. Geopolymer paste samples based on slag, showed increase in compressive strength in sodium hydroxide concentrations 6, 8 and 10 molar. Though with an increase in concentration of sodium hydroxide to 12 molar, compressive strength decreased. Also with an increase in the percentage of zeolite substitute in the source material, setting time increased but compressive strength decreased. Samples cured in 60° C temperature showed better strength, too.

Reactive powder concrete (RPC) is one of the ultra high performance concrete ( UHPC ) with superior physical and mechanical properties. Reactive powder concrete is produced using cement and very fine powdered materials including crushed quartz, silica fume and low water to cement ratio using super plasticizer. In this study, an optimum mixing ratio of RPC has been used, in which water / binder ratio ( W / B ) was equal to 0. 15 and the ratio of super plasticizer to cement ( SP / C ), was equal to 3 %. For a long time, the idea of adding fibers to various types of concrete has been considered to improve its physical and mechanical properties. In this research, by performing several experiments, the influence of adding steel fibers on the compressive and tensile strength of RPC has been investigated. The results show that the average compressive strength of samples with 1, 2 and 3 percent volumetric fibers increases about 6, 20 and 5 percent, respectively, compared to non-fibrous specimens. This increase in tensile strength is 46, 73 and 66 percent, respectively for the same amounts of steel fiber.

The present study deals with dynamic analysis of steel chimney taking rotational components of earthquake into account. The translational components of the earthquake have been used in order to obtain the rotational components of the earthquake, based on the intersecting isotropic elastic wave propagation. For this purpose, a transitional component of ground motion using frequency discrete Fourier transformed to discrete frequency and G value for each frequency determined. Then, the incident angle of the wave was calculated for each frequency. After determining the incident angle, Fourier spectrums of rocking and torsion components of ground motion were calculated. Finally, the inverse of Fourier conversion time histories of rocking and torsion components of ground motion were calculated. In order to verify the proposed methodology, the rotational components of San Fernando Earthquake were determined based on the proposed model and compared to Li and Liang's results. Then, the rotational components of San Fernando, Tabas and Taft were calculated based on the proposed model and the results were used in dynamic analysis of the steel chimneys. Finally, dynamic analyses of three model of steel chimney are presented to evaluate the effects of combined translational and rotational components on the seismic response of the dam. The deduced results show that the maximum values of displacement, stresses and shear force and also, the distribution of them have changed significantly. On the other hand, the magnitudes of these responses for different earthquakes with respect to the frequency of rotational components and the dominant frequency of the earthquake are different. The results indicate that the effects of earthquake rotational components on the dynamic response of steel chimneys are very significant. Therefore, consideration of the rotational components in the analysis of existing steel chimneys and the design of new chimneys is essential.

In this paper, the structural behaviour of precast concrete sandwich panels (PCSP) under flexure is studied. Finite element analyses (FEA) were carried out to study the behavior of composite precast concrete sandwich panels (PCSP) in order to examine feasibility of their usage as slab elements in the construction industry. The panels are composed of three layers; A high strength reinforced concrete as top layer، a thick layer of light-weight concrete as a middle layer or core and the third layer or lowest layer is a thin, flat or corrugated steel plate and or a tensile resistant reinforced concrete. In this research, at first eighth model of one-and two-way sandwich panels with the ABAQUS software was modeled and in terms of structural performance have been studied. In addition, the effect of steel shear connector’ s stiffness as measured by its diameter on the ultimate strength and the compositeness of the panels was investigated. The effect and orientation of the shear connectors in one or two directions were also investigated. The results of finite element analysis by ABAQUS software show a logical behavior of load-deflection curves in shear connectors. The ultimate strength and the degree of composite action desired were found to depend to a large extent upon the stiffness of the shear connector used.

The tuned mass damper is one of the latest structural control system that helps the structure to damp the dynamics loads. So far using the Tuned Mass Damper (TMD) on the roof or a few dampers was installed at several points at the height of the building or other levels of the building was popular, but this system has some disadvantages like considering a significant mass as overhead which requires special material and enough space to install. Therefore, in this research the efficiency of Multiple Tuned Mass Damper (MTMD) in tall building is investigated. Also the effects of MTMD on regular and irregular tall moment resisting buildings are studied. The 10, 15 and 20 story buildings with regular and irregular U and L shapes are modelled, analysed and designed, using the SAP 2000. Then the models equipped with MTMD and analysed in nonlinear dynamic mode under the earthquake records of the near and far fault, using OPENSEES. Afterwords, the models compared considering different earthquake records. finally the results showed the MTMD on the roof had seismic performance with 40% reduction of the base shear, 30% reduced absolute displacement of the stories and 35% smaller acceleration, which increased the efficiency of the models and the situation have improved their seismicity.

Consecutive loads can be a serious threat to the safety of structures. Abrupt removal of elemental elements such as columns is one of the causes of progressive failure in structures. The local breakdown caused by the sudden removal of the column can affect the behavior of the structures of successive courts. One of the loads that threatens the safety of the structure over the life of the structure is the fire. When a structure can withstand the load, one of the main factors in the safety of structures against thermal loads. Local loopholes in the structure, including the sudden removal of barrier elements, can affect the stability of structures against fire load as two successive events. In this research, the susceptibility of the RC frame to the stability of the continuous loading of the column and the subsequent fire is compared to the random variables. The 7-story concrete frame is modeled after mechanical design and is subject to the sudden removal of the column in different situations. Several parameters have been considered as random variables, and two methods of Monte Carlo and second-order second-order sensitivity analysis (FOSM) have been used for sensitivity analysis. Sensitivity analysis in a concrete frame for the analysis of dynamic duct and thermal analysis has been done separately. The results show that in the sudden removal of the column, the dead load, and in the subsequent fire scenario, the dead load and reinforcement coatings have the most sensitivity to other parameters. Also, the maximum sensitivity error of the FOSM method was calculated to be 11% compared to the Monte Carlo method.

Knowledge of subsurface characteristics has always been of interest to Geotechnical and geological engineers, especially when there is a potential risk of occurrence of subsurface anomalies such as a cavity and sinkhole. Identification of these anomalies are become more difficult at higher depths due to the reduced resolution and accuracy of recorded data. It is therefore essential to evaluate the results of both Rayleigh (R) and longitudinal (P) waves, especially for cavity in high depth. In this paper, it is attempted to investigate the ability of R and P waves to detect cavities in different depths of soil media. Also, with regard to the effects of frequency content of source load on wave field domain, various types of source load such as Ricker wavelet with central frequency of 100, 50 and 20 Hz, hammer impact and short-time impact are used. The results show that the frequency content and predominant frequency of source load have a significant effects on penetration depth and wave field resolution. Furthermore, filtering methods and separating the R and P waves could be much helpful to identify cavities in shallow and high depth by considering the wave field of the R and P waves, respectively. Hence, based on the Finite Element Modeling results, most of the source load have a good, moderate and week influence on the wave filed of soil models with cavity at depth of 2, 6 and 10 meters, respectively. Also, in case of a soil model with cavity at depth of 20 meters, P-wave has a better resolution compared to R-wave which is almost indiscernible. Generally, it could be represent that the wave field of P-wave must be considered when the depth of the cavity is increased.

Investment in construction industry is facing with many uncertainties. So, mass housing and its financing has been mostly performed by public sector. One of the mechanisms to finance in mass housing is the partnership of public-private that for its realization many challenges and obstacles have to be removed. Therefore, the research has been performed to the aim of study and prioritize the obstacles and challenges of risk management in building projects with public-private partnerships. To do so, library studies and survey method of research have been used. Statistical sample of the research includes faculty members and experts from among contractors, consultants, and employers active in the publicprivate sector partnership projects. After review and verification of questionnaire’ s validity and reliability, answered questionnaires distributed among statistical samples have been collected and related data have been analyzed through fuzzy FMEA method. The research results showed that, from among the most important obstacles and challenges in implementing risk management in partnership projects of public-private sector, reference could be made to lack of knowledge and poor understanding of politicians and decision makers regarding concept of partnership between the two sectors, as well as time consuming and difficult procedure of acquisition and possession of lands required for construction projects to be performed upon partnership of public and private sectors and banks reluctance to invest in public-private partnership arrangements.