International Journal of Civil Engineering
Volume:13 Issue: 4, Dec 2015

This paper presents an investigation on durability of alkali-activated slag mortar against magnesium sulfate attack. To do so, the immersion tests in 5% magnesium sulfate solution under room temperature and wetting-drying cycles were applied. Mortar specimens from Portland cements type 2 and 5 in accordance to ASTM standard were also prepared and used as reference. The changes in compressive strength and length of specimens were measured at different time intervals and considered for evaluating the extent of degradation. After 360 days of exposure to the magnesium sulfate solution, type 2 and 5 Portland cements and alkali-activated slag cement have shown 61, 41 and 34% reduction in compressive strength and 0.093, 0.057 and 0.021% increase in length, respectively. The specimens were also studied by X-ray diffractometry and scanning electron microscopy for characterizing the chemical products of the degradation process. Main degradation products were ettringite and gypsum for Portland cements and gypsum for alkali-activated slag cement. According to the obtained results, alkali-activated slag cement exhibits a higher sulfate resistance compared to type 2 and even type 5 Portland cements.

Gridlock is an extreme traffic state where vehicle cannot move at all. This research studies the development of gridlock by theoretical and numerical analysis. It is shown that the development of gridlock can be divided into several stages. The core of the development is the evolution of congestion loop. A congestion loop is comprised of a number of consecutively connected spillover links. The evolution of a congestion loop always tends to be stable, i.e. the state of all related links tends to be identical.. Under the stable condition, traffic states of all links are identical. A novel concept, “virtual signal” is proposed to describe the queue propagation and spillover during the stabilization. Simulation results show that congestion propagates in an accelerated way. The prevention of the first congestion loop is crucial. The achieved results have potential use for future network traffic control design and field applications.

The current research intends to study the possibility of producing fiber recycled self-compacting concrete (FRSCC) using demolitions as a coarse aggregate (crushed red brick and crushed ceramic). Steel fibers were used in recycled self-compacting concrete (RSCC) to improve fresh and hardened properties of this type of concrete. Thirty nine concrete mixes were prepared to achieve the aim proposed in this paper. Steel fiber volume fraction varied from 0 to 2.0% by the volume of concrete with aspect ratio 65. The fresh properties of FRSCC were evaluated using slump flow, J-ring and V-funnel tests. Compressive strength, tensile strength, flexural strength and density tests were performed in order to investigate mechanical properties. The optimum volume fraction of steel fibers was 0.25% and 1.0% for the mixes contained crushed red brick and ceramic as a coarse aggregate respectively. At optimum content of steel fibers, the compressive strength for the RSCC mixes with steel fibers improved by 11.3% and 31.8% for the mixes with crushed ceramic and crushed red brick, respectively with respect to control mix. Also the tensile strength and the flexural strength for the mixes were improved.

Energy conservation in buildings plays a vital role for sustainable development of societies and nations. Although, newer buildings in developing nations are being constructed using energy conservation approach, existing buildings have higher energy demand to meet the desired comfort. Excessive energy demand for cooling the built environment is a major problem over most of the arid climatic zones. The problem is predominant in all the top storied buildings which are directly under exposed roof condition. In order to reduce the overheating of the roof surface a composite combination of reflecting-cum-insulating (R-I) material was developed. The sustainable materials viz., expanded polystyrene (construction waste), saw dust (industrial waste), and the false ceiling panels prepared from industrial waste were used for the development of sustainable R-I material. The R-I material was retrofitted over the existing roof of a model room in an educational building over composite climate (Nagpur, India) and was analyzed experimentally for the period of a year. The thermal resistance of the overall roof assembly was increased from 0.28 to 0.55 m² K/W, which in turn helped to achieve 16% of the duration of the year under thermal comfort. The developed R-I material has also an advantage of low cost (INR 900 per sq. m.) of installation as well as light weight (50 kg/m²) retrofitting solution. The R-I product can further be applied on larger roof areas by the designers to reduce the cooling load of the built environment as well as increase the occupants comfort over the local climatic zone.

This paper presents a finite element analysis and its related experimental test of corrugated steel web beams subjected to fatigue loading. A particular focus in this study was set on the fatigue failure arising from the web-to-flange welded joint of the corrugated steel web beam. A detailed three-dimensional finite element model which explicitly includes the geometry of the web-to-flange welds along the corrugated web was developed to simulate the test corrugated web beam. The finite element model is verified by comparing with related fatigue experimental test results. The effective notch stress approach was also applied to analyse the web-to-flange welded joint replicating the local critical region in the corrugated web beam. The fatigue strength of the web-to-flange welded joint was evaluated and compared numerically by considering the stress distribution at potential fatigue crack initiation location. The fatigue life of the corrugated web beam was assessed numerically by incorporating material S-N relation and employing fracture mechanics approach. The comparison with the fatigue test results show that it is possible to expect the fatigue crack failure arising at the weld root or weld toe corresponding to the sections with reference angle using the effective notch stress analysis. The range of these predictions was evaluated by comparing with fatigue test results with accuracy and can be considered between AASHTO fatigue categories B and B’. The parametric notch stress analysis incorporating the influences of corrugation angle was performed and demonstrates it is possible to expect the fatigue crack failure arising at the weld root or weld toe. Finally, a practical solution for possible fatigue life enhancement of such structure is proposed by decreasing the corrugation angle or smoothing the intersection geometry of the corrugated web is suggested together with a moderate increase of the flange thickness.

In this paper, an experimental study has been conducted on strengthening of reinforced concrete (RC) connections by FRP sheets. The innovation of this research is using narrow grooves on critical regions of connection to increase the adherence of FRP sheets and prevent their early debonding. Therefore, four RC connections were made and tested under a constant axial load on the column and an increasing cyclic load on the beam. The first specimen, as the standard reference specimen, had close tie spacing in ductile regions of beam, column and panel zone based on seismic design provisions, and the second specimen, as the weak reference specimen did not have these conditions in all regions. Two other weak specimens were strengthened using two different strengthening patterns with FRP sheets one by ordinary surface preparation and the other with surface grooving method for installing FRP sheets on the connection. The results showed that ultimate load and ductility of the weak specimen compared to standard specimen decreased 25% and 17%, respectively. The shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened specimens. Also, it was observed that early debonding of FRP sheets was prevented in the strengthened connection with grooving pattern and so had desirable ductility and bearing capacity similar to the standard specimen.

The paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)2, water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime consumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view.

To study seismic performance of concrete-encased composite columns with T-shaped steel cross-section, twelve half-scale columns were tested under quasi-stastic cyclic loading. The result indicates that concrete-encased composite columns with T-shaped steel section possess good seismic performance. The failure modes include bending failure, shear-bond failure, shear compression failure and shear-composition failure. Unsymmetrical phenomenon of positive and negative hysteresis loop was shown evidently. Span ratio has a great influence on failure mode. The ductility performance decreases with increasing of axial compression level. As stirrup ratio increases, ductility and bearing capacity of columns are improved greatly, and energy dissipation capacity after yielding is enhanced. Cross tie can enhance ultimate bearing capacity, and lower strength attenuation and stiffness degradation on the later loading stage.

The paper presents a parametric numerical study on the horizontal load-bearing capacitiy of timber framed wall elements coated with single fibre plaster boards (FPB) that can be used in the construction of single- or multi-storey prefabricated buildings. The research deals with both the full elements (without any opening) and with elements containing an opening. The key behaviour indicators like the racking stiffness and strength were determined and presented as ratios dependent on the opening area. A comparative study has proved that none of the methods from the literature that were previously developed for different types of wall elements can be accurately applied to the FPB-sheated panels. It has also been shown that the methods currently available in the European design codes underestimate the capacity of wall elements with openings. Based on the results some diagrams are proposed that enable quick and efficient determination of the essential properties of wall elements with arbitrary areas of openings and may thus represent a useful tool for the structural design process.

The current building codes provide limited prescriptive guidance on design for protection of buildings due to progressive collapse. Progressive collapse is a situation in which a localized failure in a structure, caused by an abnormal load, such as explosions or other happenings. Three procedures, often employed for determination of the structural response during progressive collapse i.e. linear static procedure (LSP), nonlinear static (NSP) and nonlinear dynamic (NDP) analyses. In nonlinear static analysis, a force-based method is applied and the structure is pushed down to the target force. In this research, a new displacement-based method will be proposed for nonlinear static analysis. In displacement-based method, the structure is pushed down to target displacement instead of target force (similar to the one in seismic pushover analysis). To make a nonlinear static analysis, instead of increasing the load around the area of the removed column, a maximum displacement is calculated and the upper node of the removed column is pushed up to target displacement. Here, to determine the target displacement, results from nonlinear dynamic and linear static analyses are compared. This paper tries to present a formula to calculate the target displacement using the linear static rather than the nonlinear dynamic analysis. For this reason, 3 buildings with 3, 5 and 10 stories have been seismically designed and studied. The results show that, this method is much more accurate in comparison to the recommended approach in current codes. Also, this method does not have the limitations of force-based nonlinear static analysis.

Upstream blankets, drains and cutoff walls are considered as effective measures to reduce seepage, uplift pressure and exit gradient under the foundation of hydraulic structures. To investigate the effectiveness of these measures, individually or in accordance with others, a large number of experiments were carried out on a laboratory model. To extend the investigation for unlimited arrangements, the physical conditions of all experiments were simulated with a mathematical model. Having compared the data obtained from experiments with those provided from the mathematical model, a good correlation was found between the two sets of data indicating that the mathematical model could be used as a useful tool for calculating the effects of various measures on designing hydraulic structures. Based on this correlation a large number of different inclined angles of cutoff walls, lengths of upstream blankets, and various positions of drains within the mathematical model were simulated. It was found that regardless of their length, the blankets reduce seepage, uplift pressure and exit gradient. However, vertical cutoff walls are the most effective. Moreover, it was found that the best positions of a cutoff wall to reduce seepage flow and uplift force are at the downstream and upstream end, respectively. Also, having simulated the effects of drains, it was found that the maximum reduction in uplift force takes place when the drain is positioned at a distance of 1/3 times the dam width at the downstream of the upstream end. Finally, it was indicated that the maximum reduction in exit gradient occurs when a drain is placed at a distance of 2/3 times of the dam width from upstream end or at the downstream end.

This study simulates the temperature field and temperature stress of concrete face slabs, considering the cold waves that occur during construction as well as the contact friction between the face slabs and the cushion layer. The results show that when a cold wave occurs during construction, the surface and center temperature of the face slabs continually drop with the outside air temperature, with the surface temperature drop being the largest. In addition, the surface and center of face slabs are subjected to tensile stress, with the maximum principal stress on the surface being greater than that on the center. The maximum principal stress of the surface and center occurs at approximately half of the dam height. This study also examines the surface insulation of concrete face slabs. Surface insulation can significantly improve the temperature drop range and the maximum principal stress amplitude caused by the cold wave. A stronger heat preservation results in smaller tensile stress and an increase in the amplitude of face slabs.