مجله تحقیقات بتن ایران
سال سوم شماره 1 (بهار و تابستان 1389)

According to old structures rehabilitation problem which is included a great part of construction projects in Iran، the reusing and recycling of the debris generated by these structures is considerable. In addition، the use of waste materials along with its environm -ental aspects، necessitates the reusing of demolition wastes. Hence possibility of using these materials in concrete requires experimental evaluation. As a new type of concrete، excessive investigations are carried out on the properties of self compacting concrete (SCC). Being rheological properties as the most important issue in producing of SCC، changes in mix design require consideration of rheological properties to observe whether it is in the acceptable range. In this paper properties of the recycled concrete aggregates and their accommodation with the limitation of ASTM C33 are investigated. Then the rheology of SCC produced with recycled aggregate is compared with SCC with natural aggregate with the same gradation.

No-slump concrete is a type of concrete with slump between 0-25 mm which has wide application in the prefabricated concrete industries. The first section of this paper is dealt with introducing the ACI 211. 3 mix design method and based on this method، 32 no-slump concrete mixtures were made in the laboratory. A number of theses mixtures were made by using of silica fume and pozzolan as supplementary cementing materials and also siliceous powder as filler. Of theses mixtures، 4 mixes were elected as optimized ones. Moreover، an adaptive nero-fuzzy system called ANFIS، were utilized to predict the 28 days compressive strength of no-slump concrete. The results of the study showed that ACI 211. 3 based on the utilized domestic aggregates، has more water demand and it is recommendable to reduce the water content. In addition، by using the supplementary cementing materials like silica fume and pozzolans and neutral fillers، the consumption of cement could be reduced. Also، the results of paper indicated that the proposed ANFIS system، can predict the strength of no-slump with higher accuracy. The importance of this finding is laid on robustness of the system because of utilizing the human reasoning scheme and learning capabilities.

The moment distribution (MR) is one the most important aspects of the continuous flexural members. This importance is doubled when they are strengthened with FRP sheets. The realistic estimation of the amount of MR could be used to design of moment frames strengthened with composite sheets. Accordingly، this paper is dealt with finite element analysis towards investigating the flexural capacity and MR value of externally strengthened CFRP continuous moment frames. To this aim، 6 experimental specimens including 2 references unstrengthened and 4 strengthened samples were considered to study with nonlinear modeling of ANSYS. The variables of this study were the amounts of longitudinal steel and various cross-sectional areas of CFRP sheets. The results of the analysis are confirmed and established with the experimental observations with high accuracy. Moreover، the study is showed the effectiveness of nonlinear finite element modeling in the estimating the moment capacity and moment redistribution values of RC frames.

Polymer concrete is kind of concrete which in its mix design cement binder is replaced with polymeric resins. Application of polymer concretes was developed due to variety and quality. Nowadays، the application of these materials is limited due to high costs in comparison with Portland cement concrete. In this work، mechanical performance (compressive and flexural strengths and abrasion resistance) and depth of water penetration of a polymer concrete made of an unsaturated orthophtalic polyester resin was investigated and results was compared to Portland cement concrete (with water to cement ratio of 0. 4). Furthermore، durability of these samples in concentrated sulfuric acid was studied for 10 months. Results showed that mechanical strengths of polymer concrete are three times and two times of normal concrete''s one at early ages and at long term curing time، respectively. Severe degradation was occurred in normal concrete specimens in sulfuric acid solution after three months of exposure while 10 and 20% decrease in mechanical performance (without apparent defects) of polymer concretes was observed after 3 and 10 months exposure to sulfuric acid.

Nowadays the importance of retrofitting against earthquake is known for everybody. Since the common bylaws do not consider dynamic forces، it is necessary to retrofit the structures، using new material called HPFRCC. There are two methods to reform and strengthen one structural member that are applying steel and FRP shells. These methods have advantages and disadvantages. But HPFRCC is basically a high strength concrete containing steel، glass and carbonic fiber، not only having appropriate behavior with concrete but can increase the strength of concrete according to moment and shear forces. In this article we are going to find the highest strength concrete shell among all listed above. Finally it turned out that the steel fiber has the highest strength according to moment and shear forces. [1]

Stress distribution in lightweight aggregates concrete (LWAC) has been investigated in this research. Many studies have been already done on structural behavior of LWAC، however its properties are not well known as those of NWC. There are many provisions in different codes as equations or recommendations for designing reinforced concrete structures which are applicable for NWC. Because of different roles of aggregates in LWAC and NWC structural behavior of the LWAC needs more investigation. One of the characteristics which are applied as designing parameters is characteristic curve (stress-strain) of the concrete. In this research the stress-strain curve of the LWAC made with Scoria and Pumice has been studied. A total of 27 concrete mixes of LWAC made of scoria and pumice were tested and their stress – strain relationships have been studied. The experimental results show that rectangular stress block required to designing of LWAC structures are need more attention. The estimated flexural capacity with existing equations in codes comparison with experimental flexural capacity in LWAC is greater which lean lead to unsafety in structures. In this study، new equations for stress- strain behavior of LWAC are presented which can lead to prediction of more safe and accurate ultimate flexural strength.

Regarding the complexity of bed behavior، slab pavement and the variety of imposed load to pavement، its analysis is extremely difficult to calculate the stresses and its displacement by hand and it is unavoidable to use update utilized softwares. In this research two softwares، EverFE and KENSLAB are studied which are from jointed unreinforced concrete pavement softwares. And the results of a sample slab are compared with westergaurd analysis method by using these softwares. The model of bed in use in the softwares and in westergaurd method has been vinkler model. Hence the result comparison is possible. One of the structure model is utilized for analyzing slab is finite element that all mentioned softwares as well as westergaurd apply this method. To compare the results of these 3 methods، a slab to length 4. 57 and width 3. 65 with different thickness and 80kn loading are analyzed. This slab is evaluated with 3 states، edg loading، corner loading and loading in center slab، and some charts and diagrams are stated to consider the results of each method. It is revealed that in comparison with 3 states of loading، for slab with liquid bed in the state of corner loading، there is the most stress and by raising slab thickness، the discrepancy between the stresses will decreas in 3 loading states moreover، it is observed that in line with slab thickness، the EverFE، expresses more exact results than other methods.

A 3D FE model is generated to evaluate the effect of aggregate type on joint opening in concrete pavements، using Abaqus/Explicit. The modeling method details are presented as well. For dowel and concrete modeling، 8-node solid-brick elements are used. The concrete damage plasticity model is used for concrete plastic behavior. The interaction between dowel and surrounding concrete is simulated by surface to surface hard contact. Effect of aggregate is considered by evaluating effect on concrete coefficient of thermal expansion (CTE). The main model consists of a concrete block and dowel that is pulled out of it. Concrete shrinkage in curing stage is modeled by defining a negative thermal field. CTE for each type of aggregate is analyzed and required pull-out force a companied with required contact pressure is calculated. Finally findings show that presented model is capable of predicting the changes in contact are caused by aggregate type and increase in concrete CTE by variation of aggregate type results in greater axial force required for joint opening.

This study deals with the development of lateral load patterns for the conceptual seismic design of moment-resisting frame structures. The proposed lateral load patterns are based on inelastic behavior and are a fundamental component of a proposed seismic design methodology to limit the extent of structural damage in the system and distribute this damage uniformly along the height. These load patterns are expected to provide uniform distribution of story ductility ratios when compared to the distributions obtained with moment-resisting frames designed based on the code-compliant design lateral load pattern -s. The implementation of the aforementioned methodology would not only distribute damage along the height of the frame، but also help avoid undesirable dynamic responses that occur once structural damage is concentrated in one or in a few astories، e. g.، story drift amplifications caused by P- delta effects. The proposed design lateral load patterns are a function of the fundamental period of the structural system، the target level of inelastic behavior (or damage)، the total height of structures، and the frequency content of the ground motions.