نشریه عمران و پروژه
سال پنجم شماره 2 (پیاپی 48، اردیبهشت 1402)

Concrete can be assumed as the most regular constructional material in the world, which has a lot of advantages as well as disadvantages that attracted the attention of researchers. Adding natural materials including silica fume, fly ash, rice husk ash, metakaolin, and natural fibers and animal waste to concrete can improve the fresh and hardened properties of concrete such as slump, strength, water absorption, and durability, and at the same time reduce the environmental effects. On the other hand, adding too many natural additives can cause adverse effects on concrete, such as reducing efficiency and increasing curing time, which can be compensated by adding different kinds of fibers to the concrete mixture. In order to add natural additives to concrete, several experimental and field tests were performed, in which the effects of natural additives on the properties of concrete and their long-term performance were evaluated. Reducing the carbon footprint, and increasing resistance to cracking and corrosion are among the advantages of natural additives. In this paper, a review was conducted to evaluate the influence of natural additives on the mechanical properties of concrete specimens including compressive strength, flexural strength, and water absorption. The overall effects of utilizing natural additives on concrete properties were reviewed and listed accordingly.

According to the temporal-spatial limitation plan in Mashhad, the traffic of heavy and semi-heavy vehicles in certain areas of the city, which mainly includes the central area, is only allowed from 10:00 PM to 9:00 AM. This leads to the replacement of more light cargo vehicles with fewer heavy and semi-heavy cargo vehicles. On the other side, if this limitation plan is not applied, assuming the constant tonnage of the transported cargo, the number of pickups will decrease while the number of heavy and semi-heavy cargo vehicles will increase. However, the decrease in the number of pickups is more than the increase in the number of others. The main purpose of this study is to investigate the results of restrictions and changes in the composition of the cargo fleet from the traffic, environment and safety point of view. For this purpose, version 8.01 of Aimsun traffic simulator software was used. To evaluation of the effectiveness of the mentioned changes, two scenarios were simulated: the existing situation and the condition of not applying temporal-spatial restrictions. The results showed that in the case of applying restrictions, traffic, environmental and safety parameters are improved. But this improvement is very small. This can be seen as the result of two reasons: most of the road network in the central area of Mashhad is low-capacity with an inappropriate level of services, therefore, even if the restriction is not applied, heavy goods vehicles, except in necessary cases, don't willing to cross this area. Also, due to the weak control and the lack of enough smart equipment, the number of violations is high and this plan is not fully implemented.

Concrete strength as an important parameter can play an important role in the behavior and performance of the structure. Therefore, the use of high-strength concrete can improve the performance of the structure, of course, this is an assumption that must be checked by testing and modeling. In this article, the effect of compressive strength on the behavior of concrete structures has been investigated. In this research, three frames with 5, 10, and 15 floors, which have a system, a medium-type bending frame according to the standard (2800) and the ninth topic of the national design regulations, finally, nonlinear dynamic analysis is applied to the model. The analysis and design of frames was done with the help of ETABS software. In this study, the compressive stress parameter of concrete is considered as the main variable, and two types of light concrete with a strength of 25 MPa and 55 MPa will be considered. After obtaining the sections of the desired structure, it is coded in OpenSees software. 10 records have been used to obtain fragility curves. By examining the results related to heavy and light concrete, it can be seen that in all three studied structures (five, ten and fifteen stories), the structure with heavy concrete has less drift in the same PGA as the structure with light concrete, with an averaging of the observation results. It has been found that the structure with heavy concrete has less relative displacement in the range of 15 to 24% than the structure with light concrete.

A complex truss is a structure consisting of triangular units made up of long, narrow components that are joined at the end by a joint. Such structures are widely used in construction and industrial structures due to their ability to transmit force in long distances and spans between supports. The force of members of complex trusses, unlike simple and compound trusses, cannot be calculated using equilibrium equations alone. In recent years, Henneberg and virtual work methods that follow similar principles have been used to analyze and calculate the force of members of obscure trusses, in order to calculate the force of the members, the complex trusses have to be analyzed twice, their calculations are very long and time consuming. In this new method, there is no need to analyze the complex truss two or more times, and in a shorter time by writing less equilibrium equations and with one analysis structure, the force of the complex truss members is obtained. Another advantage of this new method is the control of calculations performed in each step independently. In addition to certain complex trusses, this method also has the ability to analyze indeterminate complex trusses and so simple hinged frame with concentrated brace, which other methods do not have this capability. This new method the force of all members is obtained with one analysis of complex truss.