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This study is a numerical investigation of the performance of reinforced concrete (RC) columns after fire exposure. This study aims to investigate the effect of introducing lateral ties and using the RC jacket on improving post-fire behavior of these columns, the effect of the duration of the fire on ultimate load of columns. The analysis was performed through ABAQUS, a 3D – non-linear finite element program. 4 m tall lengthening square RC column with a cross- section of 0.4 m × 0.4 m was used as a test specimen. The RC column was reinforced by 4Ø28 mm longitudinal bars bonded by steel tie bars of Ø10 mm spaced at 400 mm. The firing temperature was increased to 600°C for 60 min. The results indicated that as the fire load duration increases, the load’s capacity diminishes. The effect of increasing the steel ratio of the RC column resulted in a decrease in the percentage of load reduction following combustion. It was concluded that strengthening columns by RC jackets is efficient and that the axial load capacity of reinforced columns was enhanced.

Reinforced concrete slabs are among the most common structural elements. Despite the large number of slabs designed and constructed, the effect of their details on their behavior under impact loads is not always properly appreciated or taken into account. This paper describes a series of experimental studies to investigate the high-mass, low-velocity impact behavior of reinforced concrete slabs, and to provide high-quality input data and results to validate numerical modeling. The experimental scheme, which consisted of testing six sample two-way slabs with simply supported boundary conditions, was tested to failure under sequential high-mass, low-velocity impact loading conditions. The effects of different reinforcement ratios of slabs and the compressive strength of concrete on the dynamic response and behavior of reinforced concrete slabs were studied. The data indicated that the slab response is affected by the increase in the compressive strength of concrete, and it causes a clear increase in the load time history. But obviously, the load-time history is not affected noticeably by increasing the reinforcement ratio. The observed damage and crack development were found to be typical between the RC slabs. In the beginning, for slab group (1), which investigated the effect of increasing the steel reinforcement ratio, the slab with the largest reinforcing ratio was more resistant to local damage, and the cracking pattern on the bottom surface of the slab consisted of primarily discontinuous hairline cracks. The penetration and scabbing increased for the slab with one mesh S23 by ejecting the concrete around the reinforcing bars. For group (2), the decrease in the penetration and the scabbing area is observed because of the increase in the strength of concrete. For all slabs, the development of inertial forces under impact loading conditions led to observed responses and failure modes that were governed by shear.

Numerical models for impact load assessment are becoming increasingly reliable and accurate in recent years. The processing time duration for such analysis has been decreased to an acceptable level when combined with modern computer hardware. The aim of this study was to represent a simulation technique and to verify the validity of modern software in measuring the response of reinforced concrete beam strengthened by carbon fiber-reinforced polymer (CFRP) sheet subjected to impact loads at the ultimate load ranges. In this investigation, ABAQUS/Explicit Software’s nonlinear finite element modeling had been used. The response of the impact force–time history and the displacement–time history graphs were compared to the existing experimental results. The adopted general-purpose finite element analysis is verified to be capable of simulating and accurately forecasting the impact behavior for structural systems. In addition, a parametric analysis was carried out to gain a better knowledge of the performance of reinforced concrete beams under impact loading. Four parameters had been changed among the analyzed beams such as impact velocity, impact mass, CFRP sheet thickness, and compressive strength of concrete. Generally, it has been found that using a CFRP sheet in strengthening reinforced concrete beams can greatly improve the members’ impact behavior by improving stiffness as well as increasing load-carrying capacities. The enhanced performance characteristics of strengthening beams under impact loads correlate with the applied kinetic energy and CFRP thicknesses. Finally, for beams with high compressive strength, the deflection values were reduced because of the increase in stiffness.

The main objective of this study is to introduce a systematic design procedure for short-span segmental beams following a sophisticated ACI 440.2R-17 design procedure. The general aspects of innovative short-span segmental beams are easy to fabricate, economical and rapidly placed in pre-specified positions. Short-span segmental beams fabricated from individual precast plain-concrete blocks and CFRP plates. Recently, experimental tests performed on short-span segmental beams, by the authors, investigated CFRP plate-bonding, CFRP plate cross-sectional area, the thickness of plate-bonding epoxy resin, surface-to-surface condition of concrete blocks, as well as, interface condition of the bonding surface. The experimental program comprises testing of eight short-span segmental beams with an overall length, width and depth of (900, 200 and 80) mm, respectively, divided into four groups and subjected to 4-point bending test. The investigated test specimens exhibited considerable flexural strength under loading. Systematic designing of short-span segmental beams (SSSB) is presented in the current research. The advanced design method of SSSB with 1-layer of CFRP plates revealed an overestimation in ultimate strength by (73 and 15) % from the tested SSSB consisted of 1-layer CFRP/cementitious adhesive and SSSB has 1-layer CFRP/epoxy adhesive; respectively. Whereas the design method of SSSB with 2-layer of CFRP plates resulted in overestimation in strength by (71 and 45) % from the physical models of SSSB consisted of 2-layer CFRP/cementitious adhesive and SSSB has 2-layer CFRP /epoxy adhesive; respectively.

The experimental investigations were carried out to study the behavior of reinforced concrete beams strengthened by CFRP sheets under different loading conditions (pure bending, combined bending and torsion and pure torsion). The experimental work included testing twenty RC beams of the rectangular cross-section of dimensions of 160×240 mm and of 2600 mm length with an area of the ordinary reinforcement being kept constant for all beams. Two parameters were taken into consideration (Twisting to bending moment ratio (T/M) and CFRP strengthening pattern). The tested beams are divided into five groups. Each group consists of four beams; the first beam is without CFRP strengthening, the other three are strengthened with CFRP sheets of different arrangements (U-stirrups, U-stirrups and longitudinal CFRP sheets in the bottom and Full U- stirrups wrapping). Each beam is loaded to a different loading conditions (pure bending, T/M = 0.5, T/M = 1.0, T/M = 2.0 and pure torsion). The CFRP sheets were attached externally to the beam. Test results were analyzed based on the influence of CFRP on the ultimate load, vertical mid-span deflection and failure modes. In the experimental work, it was found that all strengthening patterns of CFRP sheets exhibited a significant increase in ultimate strength. This increase reached up to 78.9% for tested beams, when the beam strengthened in the form of full U- stirrups wrapping pattern for T/M = 0.5. In this study, it is observed that the use of external CFRP sheets attached to the tension sides of beams (U-stirrups and longitudinal CFRP in the bottom) could enhance the ultimate load capacity by 32.7% over the capacity of the unstrengthen control beam for T/M = 1.0.

This paper aims to provide a numerical model able to represent the behavior of reinforced concrete slabs subjected to impact loads. The nonlinear finite element analysis adopted by ABAQUS/Explicit Software was used in this study. A parametric study was conducted to provide a comprehensive understanding of the behavior of reinforced concrete slabs subjected to impact load. Two parameters were varied amongst the slabs which classified in to two groups. In the first groups, the thickness of slabs is variable, which was equal to (75, 100, 150 mm). In the second group, the thickness of the slab is constant and the variable was the reinforcement ratio, which ranged from (0.58 to 1%), per layer. In dynamic analysis, the load-time history and deflection-time relation were investigated. For the first group, obviously, as the slab thickness increased, the maximum central deflection of the slabs decreased by (48 – 84 %). Also, the impact force of the slabs increased by (40 – 106%) as the thickness of the slab increased by (33 – 100%). For the second group, the maximum central deflection of the slabs decreased by (6.6 – 8.8 %) as the steel reinforcement increased by (0.58 – 1 %). It was observed in the second group that the change in the value of the impact force was very limited. This lead to a fact that the impact force was not affected by the change of the reinforcement ratio, but mainly affected by the change of the slab thickness.

Plain Concrete pipes serve as effective underground infrastructure lines especially as sewer lines and culverts. The installation quality has a high effect on the performance of the buried pipe-soil system besides the pipe material strength. In this research, experimental investigation of buried plain concrete pipes installed in gravelly-sand soil and subjected to strip loading platform as surface loading to search the effect of the bedding compaction on the pipe. Granular soil bedding is a traditional material surrounding concrete pipes. An experimental testing program for two precast plain concrete pipes has 300 mm inner diameter was conducted in a laboratory soil box test facility. Loading on a pipes-soil system were applied up to collapse. Circumferential strain in pipes was measured by means of strain gauges in addition to the measurements of displacement developed in the vertical direction by means of a linear variable differential transformer (LVDT’s) and dials gauges. It is concluded that in case of loose bedding, a higher bedding factor of 1.83 is produced in comparison with dense bedding which produces a bedding factor of 1.49, thus yields that the quality of installation is improved with relatively loose bedding under the pipe.

The numerical investigations were carried out to study the behavior of reinforced concrete beams strengthened by CFRP under different loading conditions (pure bending and combined bending and torsion). The numerical work included analysis of eight experimentally tested beams of rectangular cross-section dimensions of (160×240) mm and (2600) mm length keeping the area of the ordinary reinforcement constant for all beams. The following parameters were taken into consideration, twisting to bending moment ratio (T/M) and CFRP strengthening arrangement. The analyzed beams are divided into four groups. Each group consists of two beams; the first beam is without CFRP strengthening, the other beam is strengthened with CFRP. Each beam is loaded to a different loading conditions (pure bending, T/M=0.5, T/M=1.0, T/M=2.0). The CFRP sheets were attached externally to the beam. Analysis results were analyzed based on influence of CFRP on ultimate load and vertical mid-span deflection. According to the numerical study, it was found that all strengthening arrangements of CFRP sheets exhibited a significant increase in ultimate strength. The three-dimensional (3D) finite element model (FEM) utilized in present work is capable to simulate the behavior of externally strengthened reinforced concrete beams by CFRP. Full bond connections (no slip) are assumed between the CFRP sheets and surface of concrete. The comparison between the numerical and the experimental results declared the validity of the numerical analysis where the range of the (Pexp./PANSYS) ratio in ultimate load was from 0.847 to 1.157. The general behavior of the (FEM) shows good agreement with the test results from the experimentally tested beams.

The paper presents results of exposure of normal concrete to elevated temperatures (400 and 700) °C covered by layers (gypsum and plaster) with different thicknesses (10 and 20) mm. The casted specimens for each type of test were divided into three groups. The first was without covering the concrete surface with gypsum, while the second and third groups were covered with gypsum of the outer surface with a thickness of 10 and 20 mm, respectively. The experimental results found that the ultimate load capacity and the first crack load of RC beams were improved by using gypsum layers through 400°C. At thickness 10 and 20 mm, the (Pcr and Pu) loss was about (8 and 6) % and (1 and 7) % respectively, compared to the concrete not covered with gypsum, the loss rate is about (25 and 13) %, and this is clear evidence of the benefit of gypsum in reducing the Elevated Temperatures directly to concrete. As for the temperature of 700, the reduction in (Pcr and Pu) was about (57 and 22) % and (31 and 16) % and (10 and 15) % at 0, 10, 20 mm gypsum thickness, respectively. Through the figures shown in the paper, which were obtained from the experimental side of the research, the load-deflection curves improved when the gypsum thickness increased during the specimens' exposure to fire. Where the relationship between them at a temperature of 400°C in a thickness of 20 mm was better than 10 mm when exposed to fire, so by increasing the thickness of the gypsum, the occurrence of deflection is less because it protects the surface of the concrete from direct exposure to heat and thus prevents the occurrence of cracks in the outer surface of the concrete.

This paper has carried out an experimental program to establish a relatively accurate relation between the ultrasonic pulse velocity (UPV) and the concrete compressive strength. The program involved testing concrete cubes of (100) mm and prisms of (100×100×300) cast with specified test variables. The samples are tested by using ultrasonic test equipment with two methods, direct ultrasonic pulse (DUPV) and surface (indirect) ultrasonic pulse (SUPV) for each sample. The obtained results were used as input data in the statistical program (SPSS) to predict the best equation representing the relation between the compressive strength and the ultrasonic pulse velocity. In this research 383 specimens were tested, and an exponential equation is proposed for this purpose. The statistical program has been used to prove which type of UPV is more suitable, the (SUPV) test or the (DUPV) test, to represent the relation between the ultrasonic pulse velocity and the concrete compressive strength. In this paper, the effect of salt content on the connection between the ultrasonic pulse velocity and the concrete compressive strength has also been studied.

Many properties of advanced materials need to be studied, including ultra high performance concrete (UHPC) as well as the Carbon Polymer Reinforcing Fiber (CFRP) rods of sand coated surfaces. The combined action of (UHPC) with (CFRP) is of constructive importance for researchers to know the behavior of the structural members in different loading stages. Eight samples were prepared with dimensions of 2.4 meters in length, 0.25 meters in depth, and 150 mm in width. The compressive strength of 110 MPa was selected after preparing many trail mixes. A computer model by ANSYS 11 program was made for the representation of all inputs, including steel fibers. All Parts of beams, testing accessories, and loads were simulated with adequate elements. The study examined the effect of the orientation of steel fibers on the flexural capacity in terms of load-deflection response. It was concluded that the distribution of the steel fibers plays a fundamental role in the behavior of the models, and thus the optimal distribution was found to be orthogonal distribution to the longitudinal direction of UHPC beam in equal ratios.

This research aims to introduce a new technique&mdash, off-site and self-form segmental concrete masonry arches fabrication, without the need of construction formwork or centering. The innovative construction method in the current study encompasses two construction materials forms the self-form masonry arches, wedge-shape plain concrete voussoirs, and carbon fiber-reinforced polymer (CFRP) composites. The employment of CFRP fabrics was for two main reasons: bonding the voussoirs and forming the masonry arches. In addition, CFRP proved to be efficient for strengthening the extrados of the arch rings under service loadings. An experimental test was conducted on four sophisticated masonry arch specimens. The research parameters were the Keystone thickness and the strengthening of the self-form arch ring at the intrados. The major test finding was that the use of thicker Keystone alters the behavior of the self-form arch and considerably increases the load carrying capacity by 79%. Partial strengthening of the intrados with CFRP fabrics of typical arch ring Keystone resulted considerable increase in the debonding load of fabrication CFRP sheets by 81%, increase in the localized crushing load by 13% and considerably increase voussoir sliding load by 107%.

Concrete beams built from individual segments connected to each other by special mechanism referred as segmental beam. The aim of this research is to exhibit a new technique for fabrication of small scale segmental beams from wedge shape unreinforced concrete segments and pultruded carbon fiber reinforced polymers (CFRP) in laminate form. Eight segmental beams including two parameters are tested experimentally. The first parameter is the area of CFRP and second is the adhesive material used to bond segments of the beams. The test shows that segmental beams have a higher ratio of CFRP area undergoes less deflection and sustain higher ultimate loading value of 38.4%. Moreover, the test of beams with concrete segments adhered by epoxy resin sustain a higher load than segments adhered by cementitious materials about 11.87%. Theoretically, segmental beams were analyzed by modified American Concrete Institute ACI 440.2R-17 report with slight modifications. The analysis results in an overestimation of flexural strength of segmental beams when compared with experimental outcomes.

This paper examines a progression of experimental studies designed to investigate the response of reinforced concrete slabs subjected to static and high-mass low-velocity impact loads. A total of ten reinforced concrete slabs were tested: three specimens were tested under static load by loading the specimens at their mid-point, and seven specimens were tested under impact load to research the high-mass, low-velocity impact behaviours of reinforced concrete slabs using a drop-weight facility. Measurements methods included a load cell, acceleration, strain in the reinforcement steel and a laser sensor to measure deflection in the centre and various quarters of the slabs (LVDT). The experimental variables included in this study focused mainly on the thickness of slab under static and impact loads, the mass of the striking object, and the height of the striking object for impact loads. The results showed that under static loads, the mean of the thickness of the slab increased by 33 to 100%, the maximum deflection at the central point decreased by 45 to 63 %, and the load capacity of the slabs increased by 77 to 265%. With respect to high-mass low-velocity impact loads, as the slab thickness increase by 33to 100%, the maximum deflection at the centre of the slabs decreased by 47.7 to 84 % and the impact force increased by 37.5 to 102%. When the height of the striking object was increased by 33 to 66%, the maximum central deflection of the slabs also increased by 24 to 72.3%, and the impact loads increased by 11 to 23.3%. Increases in the mass of the striking object by 50 to 100% led to the maximum central deflection of the slabs increasing by about 54 to 122% and to the impact loads increasing by 13 to 18.6%.

In recent years, Iraq has experienced an increase in seismic activity, especially, near the east boundary with Iran. Previous studies present their results in terms of PGA and for return periods of 500 years and less, and other studies not continued to include the whole PSHA process whereas some recent studies continued to include the whole PSHA process using earthquakes data till 2009 including dependent events. This study includes two main stages, the first is collecting the earthquakes records including the recent events till the end of March 2016 and applying data processing to get the net catalog to independent events. The second stage is applying the steps of PSHA method. Matlab programs have been built to execute these two stages and to convert the results of PSHA computations into contours of 5% damping PGA and spectral accelerations at 0.2 and 1.0 s for a return period of 2475 years, and for rock sites. Also, spectral acceleration against period has been presented for main cities. Also, the PGA map, for a return period of 475 years, has been plotted and then prepared together with similar maps of neighbor countries in one map for comparison. In general, this comparison indicates the similarity in behavior but, the values reveal a relative agreement and they are between Turkish and Iranian values.

This paper describes an experimental study on steel tube beam section as an alternative to I-section. Twelve push-out tests have been carried out on four groups consist of two section types and three shear connection types. The main objectives of these tests are to describe the connection behavior and measure the shear strength and stiffness of shear connectors. The results have been recorded and discussed, focusing on failure mode, load-slip curves, strength, and stiffness. A comparison of the test results with the ultimate shear resistance calculated from different design codes and authors was made. Experimental results showed that the current design formulas for the stud, angle and perfobond connectors with I-section can be used to calculate the resistance of shear connector with composite steel tube section. The results show that very close relations between the studs shear resistance and stiffness with I-section and circular tube. The ultimate strength of perfobond connector exceeded the ultimate shear strength of two studs due to the transverse reinforcement area through holes. The equations adopted in some common design codes can be used to determine the shear capacity of connectors with composite steel tube section.

Recently, Iraq has experienced an increase in seismic activity, especially, near the east boundary with Iran which enhanced the need to study its effect on the behavior of buildings. In this study, a comprehensive methodology was applied to investigate the behavior of a moment frame system with respect to its height after subjected to the design ground motion at Baghdad according to the recently developed seismic hazard maps and, after developing and designing the required configurations of archetype models, specifying life safety as an aimed performance level, modeling nonlinearity and applying the nonlinear static analysis (NSP) according to ASCE/SEI41-13, FEMA356 and FEMA P-695. This methodology is started by sizing members cross-sectional dimensions and applying reinforcement detailing requirements according to ACI318-14. Results show that, for a given building height and number of bays, inelastic drifts increase with decreasing the bay width because the overall building stiffness is decreased and it will be more slender, and consequently, the P- delta effects increased. Also, as the building height increased, both, target and minimum shear capacities decrease and the target displacement increases under the effect of the same earthquake ground motion. Consequently, a necessary limitation on the height of these buildings were deduced to ensure their ability to withstand the future ground shaking and, in the same time, maintaining the life safety performance level of damage. Where, it is found that the maximum allowed heights of framed buildings in Baghdad are 17, 25 and 32 stories for 6, 7.5 and 9 m bay widths, respectively.

Recently, Iraq has experienced an unprecedented seismic activity, specifically, near the east boundary with Iran which reveals the need to re-evaluate the seismic hazard at this region. This study consists of two phases. The first is collecting the earthquake records covering the recent events till the end of November 2017 including the 12 November 2017 (7.3Mw) earthquake, and applying data processing to get the net data for independent events for the study area which were more than 4300 of net main earthquakes of Mw ≥ 4 and were used in the second phase. The second phase is applying the PSHA method by dividing the study area into a grid of small cells of size 0.5 0.5°and the hazard parameters were calculated at the center of each of these grid cells then, converting the final results to contours over the study area. It is found that the values increases towards the east-northeast and north due to the continued tectonic boundary convergence between the Arabian, Iranian and Turkish plates which produces intense earthquake activity. The design spectral acceleration at 0.2 and 1.0 seconds found to be 0.33, 0.17, 0.47, 0.25, 0.71, 0.35 g for Basra, Baghdad and Erbil, respectively. The comparison between the PGA values from this study and from the seismic hazards maps from Iraqi seismic codes of 1989, 1997 and 2016, for return periods of 475 and 2475 years, reveals the continued increase with time which reveals the need to updating the seismic hazard maps continuously.

Elastic backscattering spectrometry (EBS) was performed on SiC materials, using 4He particles at energies ranging from 2 to 4 MeV, in order to establish the energy values that lead to an accurate measurement of the Si/C ratio. Analysis of the random yield of “bulk” SiC single crystals indicates that energy values of 3.25 and 3.75 MeV are the most suitable for chemical composition determination; backscattering yield of carbon is enhanced compared to the yield measured at 2 MeV, while the excitation of strong resonances above 3.75 MeV are suppressed. Random backscattering yield measurements were then carried out at an energy of 3.25 MeV on unhydrogenated SiC thin films grown on Si(1 0 0), by pulsed laser deposition, at different substrate temperatures. The Si and C atomic concentrations in the films were determined with an uncertainty of 1% and little interference from the underlying substrate. The films were found to be stoichiometric with a Si/C ratio of 1.03 ± 0.05, independent of deposition temperature, which indicates that the films were grown under congruent ablation conditions. The analysis proved to be applicable to both amorphous and crystalline SiC layers, as confirmed by the results obtained for films deposited at 400 and 950 °C, respectively.

SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 °C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 °C produces layers with increasingly uniform environment of the Si–C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 °C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp2 carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 °C, post-deposition annealing at 1100 °C reduces the spin density as a result of a more uniform Si–C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes.