نشریه مهندسی سازه و ساخت
سال دهم شماره 12 (پیاپی 77، اسفند 1402)

The project portfolio is to transfer the strategic needs of the organization to projects and operational activities. If portfolio risk occurs, it can affect the portfolio success metrics and overshadow the achievement of the organization's strategic goals. Despite the important role of portfolio risk management in the success of an organization, no proper analysis of project portfolio risks has been provided yet. The purpose of this study is to investigate the importance of portfolio risks and, selection of the best portfolio risk management strategy using multi-criteria decision-making methods. Due to the ignorance of portfolio level risks, the first step of this research is to identify and select important portfolio risks of projects based on previous studies in this field. The importance of risks in different portfolio management strategies was then assessed using a questionnaire from a group of elites. In this study, the CRITIC method, which is a multi-criteria decision-making method has been used to determine the weight of each risk, during which the importance of each risk is calculated without direct questions from experts, and only using the scores given to each risk in different strategies. After that, different portfolio risk management strategies will be identified and, the best risk management response will be calculated and selected.

Nowadays, the significance of structural design is increasingly considered especially in the structure of important buildings against blast loads due to the growing number of military attacks on structures and advancements in armament technologies. In this order, some research has been always conducted to analyze structures confronting blast loads and achieve methods for reducing the related damages. In the present research, a novel method is also presented for the reinforcement of concrete slabs and consequently, the improvement of slabs’ performance under blast loads. Instead of using steel rebars, perforated steel plates are utilized for reinforcing the concrete slabs in this method. In order to investigate this system of reinforcing the concrete slabs under blast loads, models of concrete slabs reinforced by perforated plates and by rebars with an equal volumetric percentage of steel were simulated and evaluated in the ABAQUS software under two blasting scenarios. The findings illustrated that the center of slabs has had less displacement in concrete slabs reinforced with perforated plates under blast loading caused in the air. However, some damages have been seen on the backside of those slabs as local punches in the center of the slab under the blast loading. These slabs are more prone to concrete scaling compared to the slabs reinforced by rebar. In this regard, there was an attempt to use corrugated perforated plates or utilize perforated steel ribs as stiffeners so that the interaction between concrete and the reinforcing system of the slab increases. The results also demonstrated that utilizing perforated plates with some perforated ribs can passably reduce the displacement of the slab’s center and also the damage in the slab tremendously improves.

The COVID-19 pandemic has caused numerous damages and challenges in the construction industry, in addition to taking a significant number of human lives and imposing heavy costs in the healthcare sector. These damages and challenges have undoubtedly resulted in extensive economic and social consequences for countries worldwide. Therefore, examining these challenges and providing appropriate solutions during times of crisis and widespread virus transmission is of utmost importance. In this research, a list of damages and challenges associated with COVID-19's spread on active construction projects was first compiled through library studies. Then, using a Likert-scale questionnaire, the opinions of project management experts in Kerman city were collected and analyzed in the SPSS software. The triangular fuzzy number comparison matrix was completed and the prioritization of indicators and sub-indicators was performed using the Super Decision software. Finally, the decision matrix was formed based on the multi-criteria TOPSIS fuzzy method using the criteria of "impact level," "importance degree," and "preventability of damage." The identified damages were ranked using the relevant questionnaire, and ultimately, risk management solutions were provided through appropriate responses. Based on the research findings, damages related to "financial challenges," "health challenges," "work and organizational challenges," and "time and scheduling challenges" had the most significant impact on active construction projects, respectively.

Green building is considered as an effective method for the interaction between the rapid development of construction, conservation of resources with the least impact on the environment, and the distribution of renewable and clean energy. While green building has such potential benefits, the risks associated with green buildings have been less evaluated. Therefore, the purpose of this research is to identify and rank the upcoming risks of the development and construction of green buildings in Iran, and to determine the importance of the four limitations of the project in the most effective identified risks and to prioritize the limitations in green building projects. In this research, 10 risks were identified including: economic, contractual, managerial, educational, legal, industry, functional, market, environmental and safety, by examining and evaluating the issue of the development and construction of green buildings in scientific and research sources. Then, by designing and compiling the questionnaire tool, the research objectives were evaluated in two stages. In the first step, the identified risks were ranked using the Analytical Hierarchy (AHP) method and the most effective risks were determined. During the second stage, with the aim of determining the importance of the four limitations of project management and the impact of the most effective risks on the four limitations, it was evaluated and determined by the Fuzzy Hierarchy Analysis (FAHP) method. The results of the first stage showed that the five economic, market, performance, industry and safety risks are the most effective risks for the development and construction of green buildings. The results of the second phase showed that the importance of quality limitation was the first priority, and after that, cost, time, and work area were placed in the next priorities.

In recent decades, different structural systems have been proposed to make tall buildings with suitable seismic performance. According to the art of architecture roll, especially in tall structures, and its effect on the taking attention of tourists and international investors, engineers turned towards systems that compose suitable structural performance with beauty. One of these systems is called diagrid structural system. In this paper after reviewing a number of researches conducted in this field, beside the study of seismic performance, coefficient of behavior of these types of structures are calculated by static nonlinear analysis method using SAP2000 structural analysis software. In this research, 9 structure models with the number of floors 18, 36 and 54 were modeled with three angles of 50.2, 67.4 and 74.5. By examining the results, it was observed that the mean coefficient of behavior for 18, 36 and 54 story models is about 2.70, 3.00 and 3.85 respectively. also, the results shows that using the diagrids by angles of 67.4 and 74.5 degrees, the value of stiffness is increases, and the displacement of the roof floor and the it's period decrees, also the structure is more economical in terms of material consumption, so the optimal angles should be this range, which more flexibility is created in the plan and elevation of the structure.

With the development of new engineering materials, such as shape memory alloys, their use in civil engineering applications has increased greatly. Thus, in the present study, the mechanical behavior of yielding metal dampers made from shape memory alloys in steel frames is investigated numerically. For the purposes of evaluating the seismic performance of the proposed new system, a nonlinear static analysis has been conducted using the ABAQUS software. Using Brinson's behavioral model with considering the phase transformations, as well as the Drucker-Prager failure criteria, we were able to simulate the superelastic behavior of shaped memory alloy materials, both of which were implemented in ABAQUS with the UMAT subroutine. We have continued this investigation by studying the effect of geometric variables on the performance of the system as well as the stiffness, ductility, and energy absorption capacity of the different specimens. The damper that we propose is capable of providing high energy absorption and can be easily replaced by other flowing metal dampers such as TADAS and ADAS. The proposed system shows a significant improvement in terms of ductility and energy absorption as compared to the braced frame with a corresponding steel damper, which can be used in various engineering applications.

In this paper, the reliability of steel frames equipped with fluid viscous damper (FVD) is discussed using multiple limit state functions defined based on the drift ratio and acceleration of the structure. Monte-Carlo Simulation (MCS) method has been used for reliability analysis and determining the failure probability. For numerical analysis, three steel frames of 4-, 8- and 12 -storey equipped with linear and non-linear FVDs designed based on direct-displacement method have been considered which FVDs distributed using shear-based and uniform distribution methods. By applying uncertainties in the structural and FVD parameters, for each frame the necessary number of random frames have been generated by using the Latin-Hypercube Sampling (LHS) method. The generated random frames subjected to 20 earthquake records and the time history dynamic analysis has been performed. By performing reliability analysis, the structural failure probability for single and multiple limit state functions has been determined with threshold values for maximum drift ratio and acceleration corresponding to different performance levels. The results of evaluations show that for the acceleration limit values almost corresponds to the moderate failure level in seismic codes, such as the limit value of 0.6g in Hazus-MH requirements, the increase in the probability of structure failure with multiple limit state functions compared to the drift ratio limit state function was less than 10%, while for a lower limit value of acceleration such as 0.3g, this increase is up to 87%. It was also observed that despite the fact that linear and non-linear dampers with different distributions have met the design criteria, they performed differently in reliability analysis. According to the results, it is suggested to consider the effect of acceleration-based limit state function in evaluating the reliability of acceleration-sensitive structures that have lower acceleration limit values.

Beam-to-column joints in reinforced concrete structures play an essential role in the overall behavior of the structure. Therefore, it seems necessary to strengthen joints that have been damaged over time under various loads or designed only based on gravity loads. Nowadays, shear retrofitting of joints with fiber-reinforced-polymers (FRP) has attracted the attention of researchers. Since the shear force applied to the joint is transferred by the truss mechanism formed by horizontal and vertical bars and also the compressive strength of the concrete, so the concrete of the joint plays the main role in the shear capacity before retrofitting by FRP materials. In this study, 7 reinforced concrete external joint specimens were designed and constructed on a scale of 2/3 and in two concrete compressive strength groups of 30 and 42 MPa. Seismic criteria were not considered in these joints. Two specimens were damaged up to 1.5% drift and the other two specimens up to 3% drift, and then retrofitted with FRP materials by Near Surface Mounted (NSM) method. Of the other three specimens, one with and two without considering seismic criteria as control specimens were subjected to cyclic loading at two levels of concrete strength. The purpose of considering two different levels of concrete strength was to investigate the effect of increasing concrete strength within the normal range of engineering on the performance of the NSM-retrofitted joint. As the results show, damaged retrofitted specimens with concrete compressive strength of 42 MPa were able to increase the bearing capacity of the joint by 12% compared to the seismic control specimen with concrete compressive strength of 30 MPa. Also, the increase in concrete strength by 12 MPa caused a 20, 40, and 65 percent increase in the bearing capacity, hardness, and energy dissipation ability of the NSM retrofitted specimens, respectively.

Project delivery systems, as the structure of the contract and the formation ‎of relations between the project ‎participants, create a framework for the ‎formation of contracts of different types of projects by allocating risk ‎‎among the project participants. Delivery systems can greatly affect the ‎time, financial, or quality goals of the ‎organization and are generally ‎classified into 5 categories: In house, Traditional, Design Build, Construct ‎‎management, and Public-Private Partnership (PPP). Each delivery system ‎has its own advantages and limitations, ‎which makes the choice between ‎them dependent on the project conditions and client's expectations. In this ‎article, ‎a new approach based on the allocation of contractual risks is ‎presented, with the help of which the employer can ‎choose the project ‎procurement system depending on the level of risk acceptable by the ‎employer. For this purpose, ‎by studying the records of risk allocation in ‎‎26 water projects in Iran, 14 main Contractual Risks have been ‎‎introduced, which are the basis of decision making for the project delivery ‎system. Based on his organizational ‎capacity in accepting a certain level ‎of 14 risks, the decision maker can select the appropriate delivery system ‎for ‎the project. Based on this approach, a multi-objective decision-making ‎model has been developed, which, by ‎receiving the project's risk profile, ‎quantitatively suggests the optimal structure and determines its level of ‎risks ‎exposure (in the form of an increase in the project's cost price). The ‎sensitivity analysis tool of this model also ‎guides the employer which ‎contractual tools or management capacities the employer should provide ‎in case of ‎using a specific contractual model.‎

In this paper, the pseudo-acceleration spectra of the three accelerograms of El Centro, Naghan and Tabas, which were obtained by the linear interpolation method of stimulation (Jennings’s method) and also by using the cubic spline function, are compared with each other. Jennings' method is based on linear interpolation of excitation and is acceptable for short periods of time. In this research, three accelerograms of El Centro, Naghan and Tabas were considered, and their pseudo-acceleration response spectrum (base shear coefficient) was calculated for different damping values using linear interpolation method and interpolation with spline function. The considered damping were zero, two, five, ten and twenty percent. In order to determine the difference between the linear interpolation method and the spline function interpolation method, the time interval between the accelerometer points was divided into 2, 5, 10, 20, 50, 100, and 200 equal parts, respectively. Then, once with the linear interpolation method and again with the spline interpolation method, the internal points between the internal acceleration points were obtained and their pseudo-acceleration spectrum was calculated using the Jennings method and the interpolation method with the spline function. The calculation results showed that the pseudo-acceleration spectrum values calculated by the spline interpolation method in very short periods and low damping have a significant difference with the corresponding values of the pseudo-acceleration spectrum calculated by the linear interpolation method. It should be noted that the initial time interval between the accelerogram points of El Centro, Naghan and Tabas is 0.02 seconds.

In the third millennium, cities have of a great potential as the engine of Social growth and development. Urban management, therefore, should pay attention to its internal structures and processes to achieve sustainable development In Iran, rapid population growth -with 70% of urban population- and misallocation of resources and facilities on the one hand, and financial self-sufficiency of the municipalities on the other hand, has broached more than ever a need for assessment of performance in order to improve and promote management. Considering the role of municipalities in organization of urban management, it is necessary to use scientific methods for improvement and promotion of urban management in different economical, social and environmental fields and in line with urban sustainable development. In this research, the goal is assessment of performance in Karaj Municipality and Deputies then rank ranking them. therefore, a model of Network Dara Envelopment Analysis (NDEA) technique has been used to assess the efficiency of municipalities according to internal structures. The results of the model after collecting the data by considering five input and 12 output variables illustrated that in 2014, more municipalities were efficient. furthermore, district 5 in 2014, district 4 in 2015, and districts 1, 4 and 5 in 2016 were efficient. The municipalities of districts 4, 8, 11 and 12 have achieved the best performance in the technical and civil depute during these years

Modern damage-free systems are part of modern lateral seismic structures. These structures have minimal residual displacement and dissipate earthquake energy through replaceable fuses. self -centering rocking steel braced frame systems that have been investigated in this research are considered among these modern seismic systems. In self-centering rocking structures as well as other tall structures, the effect of higher modes can cause irreparable damages in the structure. In this research, an attempt has been made to reduce the effects of higher modes by using buckling restrained columns and braces (BRCs and BRBs) as energy dissipating fuses instead of standard columns and braces in self -centering rocking structures. Five 12-story structures were investigated, including;self -centering rocking steel braced frame system and four other structure with placement of BRBs and BRCs at the base, one-third, middle and three-quarter of the height. To investigate the seismic behavior of these structures, several analyses has been performed in OpenSees software under 22 far field records according to FEMA P695. Geometric and material nonlinearities is considered in the modeling. The results show the improvement of the seismic performance and the reduction of the effects of higher modes in the case of using BRBs and BRCs in the stories, compared to the case of the common self-centering rocking bracing system.