نشریه مهندسی عمران مدرس
سال بیست و دوم شماره 1 (فروردین و اردیبهشت 1401)

This study presents the experimental results and numerical analyzes on the conical and pyramidal shell foundations located on loose unreinforced and reinforced with geogrid sand. The results have been compared with the values studied for flat circular and square foundations. Laboratory studies were performed on different types of shell foundations with different apex angles using small-scale physical modeling. In order to extend of study for determination of the effect of various conditions of foundation’s depth to width ratio and the number of geogrid layers on bearing capacity ratio, numerical analyses have been done by limit analysis method. The results have shown that, in general, increasing the depth of the foundations and the use of reinforcing structures ameliorate the geotechnical performance of foundations in both flat and shell models, although this enhancement is more evident in plane foundations. The load bearing capacity for the foundations with 180°, 120°, 90°, and 60° apex angles is put up to 40%, 36%, 32%, and 28%, respectively by rising in the foundation depth to Df/B=0.5, and is raised to 76%, 67%, 61%, and 55%, respectively by the growth of the foundation depth to Df/B=1.0. The use of geogrids increases the bearing capacity of plane foundations more than the shell foundations. The use of a single geogrid layer increased the bearing capacity of the foundations on the soil surface by an average of 79%, while the use of two layers of geogrid increased the bearing capacity by 86%, reflecting the fact that the use of two layers of geogrid will not significantly improve the bearing capacity in comparison to the condition when the soil is reinforced with a single geogrid layer. Bearing capacity of buried foundations with Df/B=0.5 is increased to 50% and 53% by using a single geogrid layer and double geogrid layer, respectively, and with Df/B=1.0 is increased to 28% and 30% by using a single geogrid layer and double geogrid layer, respectively, in comparison to foundations which are built on surface unreinforced soil. For foundations on the soil surface with 180°, 120°, 90°, and 60° apex angles, using a single geogrid layer increases the average bearing capacity to 99%, 81%, 75%, and 60%, respectively, and the use of two layers of geogrid increases to 110%, 90%, 78%, and 62%, respectively. These conditions are less pronounced for buried foundations and the increase in load bearing capacity for footings with all apex angles is about 50% for Df/B=0.5 and 29% for Df/B=1.0. The use of two layers of geogrid will have less impact on the foundations with smaller apex angles.

The plate girders used in bridges usually have a deep and relatively thin web, therefore, the buckling of the web is one of the important factors in the design of such girders. While the limit state of web buckling dominant design, Longitudinal and transverse stiffeners are used to increase cross-sectional strength. The location of stiffeners in flat girders has been extensively studied, which has led to the most effective placement for longitudinal and transverse stiffeners. In the case of curved beams in the plan is not as extensive as in the case of flat girders, especially in the case of longitudinal stiffeners in the asymmetric section. Summarized herein is a study that explored single span, horizontally curved, plate girders having a yield stress of 50 ksi (345 MPa) to investigate their flexural behavior as a function of the position of a single longitudinal stiffener at various locations along the depth of the web. The studies were conducted using ABAQUS with the girder cross-sections under high vertical bending moment and low shear. As a result of these studies, recommendations are made for positioning longitudinal stiffeners on horizontally curved:-Placement of longitudinal stiffener at distances D/4, D/5, D/6 from the compression flange can control the flexural buckling of the web. -Among the above-mentioned locations, the location of the longitudinal stiffener at a distance of D/4 from the compression flange has the best shear response in the beam. Therefore, in this study, the optimal location of the longitudinal stiffener at a distance of D/4 from the compression flange.

Wind erosion and the phenomenon of Dust with all of its controlling methods is serious problem. This phenomenon lead environment degradation and fugitive dust storms. So, Study and use of the new methods to control this natural phenomenon is essential. In this study, the novel and environmental friendly method of soil biological stabilization was investigated with using an abundant bacterial species founding in nature and soil deposits. The scientific name of this bacterium is Sporosarcina Pasturii (PTCC 1645) and uses as the urease-positive bacterium. This bacterium produce urease enzyme which converts urea to ammonium and carbonate, resulting in the precipitation of calcite crystals that bridge the soil particles. In this study a mixture of cementation and bacterial-cell solutions uniformly sprayed onto the exposed top surfaces of the soils. The concentration of bacterial-cell solution was quantified in terms of its optical density at 600nm wavelength (OD600) which equal 1.5 (that is, approximately 1.5×108 bacterial cells·ml−1). The prepared equimolar urea–calcium chloride cementation solution included nutrient broth (3g.l-1), ammonium chloride (10g.l-1) and sodium bicarbonate (2.12g·l-1) prepared at 0.5M concentration. The mixture volume sprayed onto each specimen was equal to 1.5Vv (where Vv is the pore voids volume of the topmost 3-mm thick layer of the 20–mm deep loose sand tray-specimens). The bench scale experimental programme presented investigates the proposed technique’s effectiveness for stabilisation of two clean, angular to sub-angular medium silica sands and carbonate silty sands with different gradations (sand t60 and sand t90 with size ranges of 0.125–0·50 and 0.075–0.85mm, respectively and carbonate sand with size ranges of 0·001–0·85mm, and mean particle size (D50) values of 0.28, 0.24 and 0.20 mm, respectively), the time-dependent (retention time 3, 7, 14, 20 and 28 days) compressive strength development for the crustal sand layer following single- and double-MICP (with interval of 6 days) spray treatments, as well as wind tunnel experiments under the condition of wind velocity of 20 ms-1. The effect of dew formation on crustal compressive strength development with curing period and the efficiency of the MICP treatment for the outdoor environment compared to laboratory-controlled test conditions. A pocket penetrometer was used to determine the compressive strength of soils. Significant improvements in the Compressive strength of the treated soil samples were observed. The results show improving compressive strength with time. The highest compressive strength in the carbonate sand was obtained equals to 84 kPa. Silica sand with finer size distribution has shown more compressive strength than two other soils. Also the results showed that double-MICP spray treatments of the bacteria solution and cementation was more effective than single- MICP spray treatments in the compressive strength of soils, especially in the silica sand equals to 190% in a curing period of 28 days. Also, the cured MICP-treated crustal sand layer was stable to 20 m·s−1 winds that demonstrating the potential of biological stabilisation via the MICP process as an appropriate option for dealing with desertification and motion of sandy soil deposits.

There are many sources of aleatory uncertainty in the design of RC structures. Contrary to what is commonly thought, to assessment the safety of RC structures, the parameters related to the resistance of structural members and loads are non - deterministic, so that the description of the actual behavior of the structure without considering the uncertainties in these parameters will be impossible. The safety and performance of a RC structure is a function of the safety of its components, especially columns. Therefore, estimating the safety of RC columns with respect  to these sources of uncertainty seems necessary and the inevitable result of inattention to it is a risk that threatens the expected performance of the structures.  Achieving this goal is possible by analyzing reliability, through which various sources of uncertainty can be considered by applying probabilistic mathematics and a systematic process during the analysis and design process, and the achievement of the desired functions can be quantitatively evaluated. In most studies on the reliability of RC columns, the uncertainty in the load eccentricity is ignored and the load eccentricity is considered a deterministic and fixed  quantity. the fixed eccentricity criterion means that the axial load and the bending moment are perfectly correlated and a linear relationship is established between them. When axial force and moment are perfectly correlated, this does not cause any problems; but when this is not the case, the reliability analysis results are only approximate. In fact, axial force and bending moment are not perfectly correlated in many cases, so to assessment the safety of RC columns, it is necessary to consider the uncertainty in the load eccentricity. Identifying and determining the relative importance of each of the uncertainties in the analysis of the reliability of the columns is an interesting and important issue, so that according to the results, can be seriously focus on the very important sources of uncertainty  and  Considered other uncertain parameters with their best estimates. Such an approach significantly reduces computational efforts and will be very practical and useful for large and real civil infrastructure. In this research an efficient approach for modeling sources of  uncertainty in the safety assessment of RC short column with square and rectangular sections is proposed based on the first - order reliability method ( FORM ). In the proposed approach, limit state function is defined according to the interaction effect of axial force - bending moment of the column and considering modeling error which is a function of load eccentricity. The results show that various parameters such as correlation, cross-sectional shape, longitudinal reinforcement ratio of steel, load ratio, load eccentricity  and distribution of longitudinal reinforcement in cross section are very influential on the values of the probability of failure of the column. Finally, according to the results, the coefficients of importance for identifying the most important parameters affecting the probability of failure of sample columns at various load eccentricities  were presented which demonstrate  that the compressive strength of concrete, modeling error and live load compared to other variables are of the greatest importance, which should be considered in the design and implementation of this important point.

Frames with masonry infill are the most common type of structures used in developing countries. Masonry infill affected the initial stiffness and strength of reinforced concrete buildings. The presence of opening in masonry infill is often used for placing doors and windows and it may reduce the seismic performance of the RC frame structure. Nowadays, the impact of the frame and infill on structure is one of the challenges in engineering researches. Engineers generally ignore infill in designing the building and consider it as non-structural part. When the masonry infill is placed in the concrete frame, significantly changes its mechanical properties, the stiffness and strength of the structure increase and ductility of the concrete frame reduce. There is interaction between masonry infill and itchr('39')s frame, so, the frames with infill behave differently than those frames without infill. Disregarding the effect of masonry infill, they can be safe and reliable in terms of resistance in design, since the increasing strength around frame has a positive effect on earthquake strength and overall structural stability, however, it should also be considered that masonry infill will increase the stiffness of the infill-frame and larger portion of the lateral load would attracted by frames. This can be a negative factor when ignore the infill masonry in the design. In the present study, by numerical modeling by nonlinear finite element method, the effect of the presence of masonry infill with different door and window openings on the behavior of concrete frames with seismic and non-seismic details at different axial load levels and different masonry infill thicknesses in seismic performance of frames concrete has been examined. For this purpose, the proposed models are first validated using laboratory results in ABAQUS finite element software. The results of the analysis show that increasing the axial load increases the final strength, effective stiffness and reduces ductility in specimens with masonry infill with different opening of doors and windows and reinforced concrete frame with seismic characteristics. The ultimate strength in specimens with reinforced concrete frame with seismic characteristics shows a slight increase compared to similar samples with reinforced concrete frame with non-seismic characteristics, which can be ignored. Increasing the thickness of the specimens increased the ultimate strength and effective stiffness of the specimens with seismic and non-seismic details. The results of these studies show that the different positions of the openings have significant effects on the behavior of the frames. If the opening is large or moves away from the center of the masonry infill, the final strength drop and stiffness effective reduction will be more.

Today, the use of different kinds of polymer, as the modifier of some repair mortars properties, is growing. Given the damages to concrete structures, it is necessary to use appropriate repair layers. In concrete structures, concrete and steel are connected, and in most cases, repair layers are applied in direct connections with steel. Therefore, in this research, the shear and tensile bond strength between steel and styrene-butadiene rubber polymer modified mortars was measured using semi-destructive friction-transfer and pull-off tests. In the "pull-off" test, to determine the bond between the mortar and the steel, a core with a 50mm diameter and is first mounted on the test surface using a diamond drill bit and a metal cylinder with a diameter of 50 mm and a thickness of 20 mm is attached to the partial core. Then, the tensile force is applied to the cylinder by means of a "pull-off" device to make the partial core fail. To measure adhesion with friction transfer method, first a small core was created from the mortar surface to the steel substrate surface using the coring machine. Thereafter, the friction transfer metal device was fixed onto the core and the torsional moment was applied using a typical torque wrench in order to cause failure in the core. Moreover, the effect of polymer on the shrinkage of mortar was evaluated. Shrinkage is one of the important problems that negatively affects the adhesion of repair mortar and steel. Due to the fact that hydrated cement paste has capillary pores that contain some water, shrinkage occurs after this moisture leaves the pores. The effect of polymer on mortars was investigated by taking images with a scanning electron microscope and using the “Image-J” and “Origin” software programs. Afterward, in order to evaluate the mechanical properties of mortars, the in-situ compressive and flexural strengths of the mortars were determined, and the calibration curves were plotted by comparing them with standard laboratory tests. Then, relationships were proposed to convert the results of in-situ tests to the compressive and flexural strength of the polymer modified mortars. Eventually, the cracks and stresses that appeared in the mortars were provided using ABAQUS software. The obtained results indicated the effect of polymer in reducing the shrinkage of mortars and increasing the shear and tensile bond strength between steel and mortar, along with a high correlation coefficient between the measurements in the in-situ and laboratory tests. Comparing the modified mortars with polymer and ordinary mortar, it is observed that at the age of 90 days, adding 10, 15 and 20% of SBR reduced the amount of shrinkage to 35.3%, 4.2% and 45.4%, respectively. Addition of styrene butadiene rubber to the repair mortar increased the shear bond strength obtained from the "friction transfer" test between the mortar and steel at the ages of 7, 42 and 90 days by 44.4, 178.2 and 303.1%, respectively. Adding SBR to the repair mortar increased the tensile strength of the "pull-off" test between the mortar and the steel at the ages of 7, 42 and 90 days by 58.7, 183.4 and 291.2%, respectively. A good agreement was also observed between the numerical and experimental results.

Most members of structures whose useful life has elapsed need to be repaired. These members may be damaged by a variety of factors. Due to the high cost of reconstruction, a large portion of countries’ development budgets are spent annually repairing and rehabilitate these structures. Compressive members such as columns are one of the most important components in a structure that play a major role in bearing and transporting all the vertical and lateral loads of the building. Basically, no column can bear to its fullest capacity and is failed by buckling. As a result, many researchers are interested in retrofitting and increasing column strength using new materials and methods. In this investigation, damaged circular hollow section steel columns with vertical and horizontal notches and different percentages of 25, 50, 75 and 100% were examined, also the effects of Carbon Fiber Reinforced Polymer (CFRP) for strengthening has been studied. 26 specimens of steel Circular Hollow Section (CHS) column with the same height and different damage dimensions under compressive load were analyzed by ABAQUS 2016 software. The main problem with slender columns is the global buckling under compressive loads. In order to improve the accuracy of the analysis, a combined method was used to study the post-buckling of the plastic zone. For this purpose, the specimens were first subjected to elastic buckling analysis and then Riks non-linear analysis with global and local imperfections was conducted. The results showed that the defect reduces the bearing capacity and rigidity of the steel columns and horizontal defect is more effective in reducing ultimate load in compare to vertical damage. Horizontal-defective columns experienced ‎significantly lower load bearing capacity than ‎vertical-defective columns and can reduce final load up to 52% ‏ in 100% damage, which this reduction indicated that by increasing damage along the perimeter of the column section, final load decreased sharply. The results also showed that it is critical when the deficiency zone is entirely destroyed, while the effect of damage less than 25% was maximum 2.66%. Columns failure occurred in the form of global and local buckling; in all cases global buckling emerged in the form of the column bending, but the local buckling was different according to the type of the damage. ‎Failure modes of the control column is global ‎buckling with focus on the middle of the ‎column, for non-strengthened specimens with ‎horizontal and 100% damage, local buckling‎‏ ‏is shrinkage of ‎notch edges and for vertical notch is defect ‎edges opening. In specimens with a lower percentage of damage, local buckling occurred for horizontal defects in the form of the inward buckling on the middle and for the vertical ones was outward buckling. ‎Strengthening of columns retrofitted with CFRP presented that these kind of fibers have a positive effect on significant gaining ultimate load capacity, delaying defect buckling, controlling fractures and reducing stresses at the damaged area. CFRP strengthening of defected cases using 4 layers, restored the reduction of ultimate load up to 51%, which shows the proper performance of the fibers in retrofitting.

Due to the significant advantages of the performance-based seismic design method, such as the possibility of determining the possible damage and financial and human losses of residents and neighbors of the structure, this method has been widely welcomed. However, since this method requires more sophisticated analysis than conventional force methods, sometimes the simple force method is preferred by some professional engineers. The main purpose of this article is to combine the two methods of force-based and performance-based and to develop a hybrid method in order to use the advantages of both methods.in this regard, frames with 3, 6, 9, 12, 15 and 20 story with 3 bays with a width of 5 meters have been considered. The length of the link beam is defined as another parameter affecting the response, 1, 1.75 and 2.50 meters. The studied models have been developed by designing the method of load and resistance factor design method, for 3 performance levels of immediate occupancy, life safety and collapse prevention, as well as the first occurrence of the plastic joint. The final models are analyzed under 20 pulse-type near-fault records using time history analysis. To generate the expected database, 12,960 time history analyzes were performed based on an incremental dynamic analysis platform. In this regard, a unique frame is continuously and repeatedly affected by a single accelerometer by multiplying the accelerometer by an SF coefficient. In each iteration, the maximum displacement in the frame is compared to the target range of ASCE41-13 code. The analysis operation is continued until the expected numbers are reached and then stopped. For each of the frames, 4 different acceptance levels are defined to consider different performance levels. Finally, using the genetic algorithm, the corresponding experimental relationships are presented to determine the behavior factor, local and global ductility. The proposed relationships are influenced by geometric characteristics such as the number of stories, the stiffness ratio of the columns, the slenderness of the braces, the length of the beam and the ductility levels. The first ambiguous issue that has been less mentioned in previous research is the use of near-fault field records in the development of a hybrid functional seismic design method. After generating 12960 data from an innovative time history analysis, two intelligent adaptive neural-fuzzy models have been used to calculate the coefficient of behavior and ductility of the structure. In order to create the best and most accurate model, Fuzzy C-Mean clustering (FCM) and Subtracting clustering methods have been used. Based on the results, the model created based on Subtracting clustering provides more accurate results than the other model. The results of hybrid seismic design in comparison with the force method and equivalent time history show the acceptable accuracy of the method introduced in the field of hypotheses. The obvious advantage of using a hybrid seismic design method compared to force methods is the possibility of selecting an expected performance level, which leads to design control and more accurate estimation of response values of quantities such as global ductility, local ductility, inter-story drift

Structures get local damages by passing time during the service period under environmental conditions and loads, although insignificant. It is essential and important to maintain the health, durability and proper performance of structures and their various parts and lack of proper recognition of the behavior of structures may cause spontaneity damages and consequently, high social and economic costs may occur. According to the proper performance of CFST columns, using this type of columns in high-rise buildings and bridge structures has expanded especially in seismic areas. Steel and concrete can cover each otherchr('39')s weaknesses by simultaneously using concrete and steel in CFST columns. The weakness of concrete against tensile and the weakness of steel against pressure has compensated by the combination of steel and concrete in this type of columns. Also these columns may be damaged during construction or after experiencing load periods (earthquake, wind, etc.), because getting structures damage is inevitable. One of the primary goals of Structural Health Monitoring (SHM) is damages detection of the structure in the early stages of formation. If the damage locations in the structure can be determined and its gradual course can be observed, the damaged members can be repaired or replaced before reaching the critical condition and occurring complete breakdown. Among the methods of damage detection, many researchers consider the methods based on signal processing. One of the methods of signal processing is the mathematical method of wavelet analysis. By using wavelet analysis, more information can be obtained from the intended signal based on its ability to localize the signal in both time and frequency domains. One of the most probable damages in CFST columns is the debonding of the concrete core from the steel tube. In this paper, the CFST column element was modeled and frequency analyzed in ABAQUS finite element software in two conditions including damage and no-damage. The effect of the debonding was considered by decreasing the modulus of elasticity of the concrete in the damage places with depth of 3 mm. The results of the analysis have shown that the information of the mode shapes of the damage and no-damage conditions (angle between the mode shape vectors and the frequency values) changes due to the effect of the damage. In order to identify the debonding damage locations, in the Continuous Wavelet Transform (CWT) detection algorithm, the input signal was defined as the sum or difference of the mode shape of the damage condition and the mode shape of the no-damage condition based on the angle between the damaged and no-damaged mode shape vectors. The results showed that the output signals obtaining from the details of input signal wavelet analysis have useful information to identify the debonding locations of the concrete core from the steel tube and at high scales, the locations of the debonding damage identify easily, and at low scales, more convergence of wavelet coefficients is observed in the locations of the damage. According to the results, the proposed method was introduced as an effective detection method of debonding damage in CFST columns.

Civil structures may experience unexpected loads and consequently damages during their life cycle. Damage identification has been a challenging inverse problem in structural health monitoring. The main difficulty is characterizing the unknown relation between the measurements and damage patterns. Such damage indicators would ideally be able to identify the existence, location, and severity of damages. In order to solve such problems, biologically inspired soft-computing techniques have gained traction. The most widely used soft-computing method, called neural networks is designed such that it can learn from data without a need of feature design process. Damage pattern can be detected using neural network. A deep unsupervised neural network can recognize patterns and extract features from data. In this paper a methodology is described for global and local health condition assessment of structural systems using vibration response of the structure. The model incorporates Fast Fourier Transform and unsupervised deep Boltzmann machine to extract features from the frequency domain of the recorded signals. Restricted boltzmann machine is a shallow neural network with two layer. First layer of restricted boltzmann machine called input layer and second layer of restricted boltzmann machine called hidden layer.Deep Boltzmann machine created by setting some restricted Boltzmann machine sequentional. Hidden layer of each restricted boltzmann machine is input layer of next restricted boltzmann machine. Each layer of restricted Boltzmann machine extract features form input data Recorded data divided to smaller vectors. Fast fourier transformation used to transform divided vectors into frequency domain.  A benefit of the proposed model is that it does not require costly experimental results to be obtained from a scaled version of the structure to simulate different damage states of the structure and only vibration response of the healthy structure is needed to training deep neural network. The input consists of a set of records obtained from the healthy state of the structure and another set of records with unknown health states. The model extracts information from both healthy and unknown sets to determine the health states of the unknown set. The healthy records are low intensity vibrations of the structure at least in one planar direction in the healthy state in the form of time series signals and The unknown records are low intensity vibrations of the structure on unknown state of health. Ambient vibrations can be due to wind, traffic, or human/pedestrian activities. An appropiate health index is defined and calculated for each part of the structure. The value of this index is between 0 and 1. The closer the value is to 1 the healthier the structure. To evaluate the efficiency of the proposed method a building structures with 35 story has been simulated in OPENSEES. Data collection should be selected appropriately to prevent errors. Obtained result demonstrate that proposed method has about 95 percent efficiency to predict damages and their severity. Different damage state put on due to three earthquakes with different severity. Structural health index calculated after each earthquake. Calculated structural health index demonstrate efficieency of proposed method for detecting damages and severity of damages.

Reinforced concrete structures with standard steel rebar are vulnerable to corrosion and harsh environmental conditions, hence RC structures reinforced with fiber-reinforced polymer (FRP) rebar were commonly used these days. Du to FRP rebar’s better performance such as high strength, low self-weight, electromagnetic transparency and, as mentioned, non-corrodibility nature, using them as reinforcing bar is very widespread now. Because of financial matters, between different kinds of FRPs, GFRP is a better choice. Considering GFRP’s high strength and elastic behavior until failure, Although a large amount of reinforcement ratio is needed in composite beam components, the flexural stiffness of GFRP rebar reinforced beams is relatively lower compared to steel-RC, and more deflection and cracking are allowed in the serviceability design of these beams. Recently, shear and flexural behavior of continuous concrete beams reinforced with GFRP bars has been well investigated. Because of linear elastic behavior of GFRP materials until failure, considering moment redistribution in analysis and design of these beams is not allowed in almost all of cods and guidelines. Although many experimental and numerical researches investigated the moment redistribution in FRP-RC continuous beams with rectangular section, the behavior of these beams with T-section is almost unknown. This paper is a numerical investigation of existence and variety of moment redistribution in concrete continuous T-section beams reinforced with GFRP bars using finite element method with ABAQUS software. The verification of numerical models was done with some experimental beams, so the simulation can be used for further researches. The considering variables included the longitudinal reinforcement percentage, the number of main bars with constant bar ratio, transverse reinforcement ratio, stirrup space with constant ratio and constant bar size. For investigating mentioned parameters, 35 beams were modeled in software according to Canadian design and construction of building structures with FRP code, so 5 groups of beams were made which one beam is constant in each group. T-section beams were modeled assuming which failure happens because of concrete crashing not rebar failure. Deflection and serviceability were not interested, so bond-slippage behavior of GFRP rebar with concrete is not considered in modeling. Problem is indeterminate, so the percentage of moment redistribution was determined by comparing the reactions resulted from numerical and elastic analysis. Load-deflection and load-moment redistribution curves were used to discuss. The results show, as there is in steel-RC structures, moment redistribution exist in GFRP-RC continuous beams with T-section; however the amount of it is lower. Amount of bars between 2.5 times of balance reinforcement ratio and 3.5 times of it, in top and bottom of beam, shows the highest flexibility load and moment redistribution capacity. Increasing the number of main bars with constant reinforcement ratio and increasing the stirrup space with constant transverse reinforcement ratio reduce the moment redistribution capacity. It seems that the minimum amount of transverse reinforcement considered in Canadian code is not enough for preventing shear failure in these beams. So, with considering some points, the moment redistribution can be taken to account in analysis and design of GFRP-RC continuous beams with T-section.