Showing papers in "International Journal of Civil Engineering in 2018"

Property Assessment of Hybrid Fiber-Reinforced Ultra-High-Performance Concrete

Abstract: The purpose of this study was to determine the effect of steel/polypropylene hybrid fibers on the mechanical properties and microstructure of ultra-high-performance concrete (UHPC). Tests were carried out on UHPC without and with fibers (steel and/or polypropylene in amounts of 0.25–1%). In this study, granite or granodiorite coarse aggregate with a grain size of about 2/8 mm was employed. The three-point bending tests displayed prolonged post-peak softening behavior. In addition, increasing the content of polypropylene fibers reduced the fracture energy. Moreover, the SEM results illustrated that adding a certain amount of fibers to concrete considerably changes the microstructure. It was observed that the smallest micro-cracks in the interfacial transition zone between the paste and aggregate occurred in the concrete containing steel fibers.

Modeling and analysis of the impact of BIM-based field data capturing technologies on automated construction progress monitoring

Abstract: Leveraging automated field data capturing technologies and Building Information Modeling (BIM) for site status analysis would play a more significant role in advancing decision-making in construction projects if applied to the traditional progress control. Despite the numerous advances in project progress control technologies, 3D modeling, and BIM execution, there is still a lack of awareness regarding the impact of these technologies on the overall performance of the projects, leading to the use of time-consuming and ineffective monitoring processes by the companies. For this reason, this study proposes a model for BIM-based field data capturing technologies and analyses the impact of field data capturing technologies on automated project progress monitoring comparing 3D model and BIM workflows. The empirical data were collected through a computerized self-administered questionnaire (CSAQ) survey conducted to contracting and engineering consulting companies operating in the Middle East, Mid-Asia, Europe, North America, and the Far East. The structural equation modeling (SEM) method was used to test the hypotheses and develop the skill model. The study confirms the importance of using field data capturing technologies with BIM in two main stages (modeling and execution) to enhance automated project progress monitoring performance. The study highlights the need for further exploration of the role of BIM-based field data capturing technologies in improving automated construction project progress monitoring.

Mix Design and Recycled Aggregates Effects on the Concrete’s Properties

Abstract: An experimental program was carried out to study the properties of concretes with C25/30 and C35/45 resistance classes designed using natural aggregates and recycled ones provided from construction and demolition waste (C&DW). Eight mixtures were prepared with different incorporation ratios of fine and coarse recycled aggregates. The physical and mechanical characteristics were measured and their evolution regarding to the paste volume, the equivalent replacement ratio and the quality of the interface between recycled aggregates and new paste has been investigated. Scanning Electron Microscopic observations have revealed a good quality of the interface. It was found that water porosity is more dependent on the equivalent replacement ratio than on the volume of the new paste. The same conclusions are reported for the electrical resistivity which has been related to the water porosity. Based on experimental results, it has been found that the Archie’s law predicts the electrical resistivity as a function of water porosity for all type of concrete. The effect of mix design parameters and aggregates properties on the compressive strength has been investigated and a model is proposed on the basis of Feret’s expression through experimental results and data points available in the literature. The modified expression is related to the aggregate fragmentation resistance expressed by the Los Angeles coefficient (LA). The Feret’s coefficient can be taken equal to 6.4 if LA ≤ 20% and it is inversely proportional to LA otherwise. With regard to the splitting tensile strength, it can be correlated to the electrical resistivity through a power law relationship. The elastic modulus, the peak and the ultimate strains are than rewritten as functions of the compressive strength and the replacement ratio to model the full stress–strain curve under uniaxial compression. Furthermore, the validity of using EC2 to model the evolution of all mechanical properties with age is ensured.

Critical External Risks in International Joint Ventures for Construction Industry in Pakistan

Abstract: International joint ventures (IJVs) are both advantageous and challenging due to differing technical abilities, economic and political environments, and cultural and legal frameworks. This study identifies the external risks particularly political, economic, legal, social and environmental in IJVs carrying out construction projects in Pakistan. It further analyzes the impact of these risks on the project success criteria of time, cost and quality. Data are collected using questionnaire-based survey and with the help of factor analysis, 16 critical external risks are identified. The top most critical risks are fluctuation in exchange rate, weather systems, political instability and delay in approval. Analytical Hierarchy Process is applied to prioritize critical external risks discretely for project success criteria. As a result, time is found to be the most influenced project criterion by the critical external risks, followed by cost and quality. The results are of importance for local practitioners in the form of recommendations for better management of IJV risks. Future research can benefit from incorporation of more dimensions of project success.

Best Value Contractor Selection in Road Construction Projects: ANP-Based Decision Support System

Abstract: Based on the limitations of traditional procurement, this study uses analytical network process (ANP) for contractor selection. Using extensive literature review, best value (BV) contributing factors are identified. Experts are involved to get their feedback for shortlisting the identified factors. An ANP-based decision support system has been developed using data collected through a detailed questionnaire survey in the local construction industry for evaluating the selection process. Further, five case studies of completed road construction projects have been used to validate the decision support system. The findings indicate that in almost all the cases, the traditional procurement system, owing to its stringent prequalification measures, subliminally took into consideration the overall value proposition, and only one case study showed anomalies for which detailed reasoning is deliberated. This highlights the tendency of practitioners to overweigh the cost-based criteria, despite an established significance of other factors, treating the intangible value factors of quality, health and safety, environmental impact, etc. as less important. It reflects that the local construction industry attaches marginal value to qualitative factors. The construction industry will benefit from implementation of BV procurement system and a prolonged exposure may help improve its value system to realize the contribution of non-cost-based factors.

The Vessel Scheduling Problem in a Liner Shipping Route with Heterogeneous Fleet

Abstract: Increasing volumes of the international seaborne trade force liner shipping companies to improve efficiency of their operations to remain competitive Many of liner shipping companies continue increasing size of their vessels, as larger vessels provide lower voyage costs per container due to their economies of scale Larger vessels also allow liner shipping companies more efficiently share the demand with the alliance partners Nowadays, many of liner shipping routes are served by vessels of different types (eg, small, medium, large) However, the key assumption of studies on vessel scheduling, conducted to date, is homogeneous nature of the vessel fleet (ie, all vessels in the fleet, serving a given liner shipping route, have the same technical characteristics) This study proposes a novel mathematical model for the vessel scheduling problem with heterogeneous fleet The objective of a mixed integer non-linear model is to minimize the total vessel turnaround cost Due to high non-linearity of the proposed mathematical model a non-linear optimization solver is used to solve it Numerical experiments are performed to evaluate efficiency of the proposed solution approach and the novel methodology Results demonstrate a computational efficiency of the adopted solution approach Furthermore, vessel schedules are found to be more sensitive to introduction of larger vessels in the fleet as compared to increase in the unit bunker cost

Effect of Carbon Black on the High and Low Temperature Properties of Bitumen

Abstract: In the present study, the effect of carbon black (CB) as an additive on resistance of bitumen to delay or prevent rutting and low temperature cracking was investigated. For this purpose, different amounts of CB (0, 5, 10, and 15 wt%) were added into bitumen with PG 58-28. Conventional tests (penetration, softening point, Fraass breaking point, ductility, and kinematic viscosity) and Superpave binder tests (rotational viscosity, dynamic shear rheometer, and bending beam rheometer test) were carried out to determine the physical and rheological properties of pure and modified bitumens. In addition, high and low temperature performance grades of pure and modified bitumens were identified according to Superpave binder specification. The results indicated that the addition of CB increased the stiffness and resistance of bitumen to rutting at high temperatures and resistance to thermal cracking at low temperatures of bitumen. Finally, the bitumen becomes more elastic and less susceptible to temperature changes.

Numerical Simulation of the Flow and Local Scour Process around Single and Complex Bridge Piers

Abstract: The present work is focused on the flow and clear-water scour process around single and complex bridge piers using the computational fluid dynamics (CFD) approaches. In CFD, the use of large time steps may accelerate the simulation process but the effects of the unsteady flow structures may not be considered in the computations. In this case, the computational method is defined as a steady-state solution. In the present study, the capability and accuracy of the steady-state solution of the flow equations are investigated by employing the SSIIM code which is numerically stable for large time steps. For this purpose, several simulations were performed for different piers and bed configurations and the corresponding numerical results were compared with experimental ones obtained from referenced bibliography. Overall, the steady-state solution of the flow equations could predict fairly well the scour geometry at the upstream side and lateral sides of the bridge pier but not downstream side of the pier. Moreover, the local scour around a single pier was also predicted by performing an unsteady-state solution (where the vortex shedding effects are taken into account) by using the Flow-3D code. The major difference between the results from the two mentioned CFD codes was observed downstream of the pier such that, compared to the physical model, the scour depth was under-predicted by the steady-state calculations while it was over-predicted by the unsteady-state calculations.

Investigating the Use of Nano Coating Over the Aggregate Surface on Moisture Damage of Asphalt Mixtures

Abstract: One of the methods to improve adhesion between asphalt binder and aggregate and to reduce moisture susceptibility in asphalt mixtures is aggregate treatment using suitable coats which cause to change aggregate polarity. In this study, effect of nanomaterial coating on aggregate over moisture damage of HMA by means of thermodynamic and mechanical methods has been probed. Aggregates used in this study are granite and limestone that have been modified using iron oxide and aluminum oxide nanoparticles. Results illustrate that in comparing modified samples through nanoparticles with control samples, tensile strength ratio on moisture condition surpasses dry condition. Surface free energy result shows that aggregate coat with nanoparticles leads to decrease in differences between free energy of adhesion in moisture condition and dry condition, and thus, stripping event is diminished. Nanoparticles’ positive performance of iron oxide compared with aluminum oxide nanoparticles in decreasing the moisture sensitivity of asphalt mixtures built is more evident about either kind of aggregates.

An Experimental Investigation on Effect of Adding Natural and Synthetic Fibres on Mechanical and Behavioural Parameters of Soil–Cement Materials

Abstract: Soil–cement is a mixture of Portland cement, soil and water that sticks together due to the hydration of the cement and compression of its components to create a dense, durable compound, which has low permeability and is resistant to erosion. Unfortunately, these mixtures do not perform well under tensile load because soil–cement materials are brittle. In this study, three types of fibres were used to reinforce the materials to compensate for this flaw: jute (a natural fibre), polypropylene, and steel (a synthetic fibre) fibres. These fibres were randomly added to the soil–cement mixture in three percentages (1, 2, and 3%). Tests were then conducted on three different soil–cement gradations each with three fine contents of different mineral types (nine different gradations in total). First, sand equivalent and Atterberg limits were conducted on the soil samples. Then compaction, unconfined compression strength, indirect tensile strength and flexural tests were conducted on the soil–cement samples in two conditions: control (unreinforced) and reinforced soil–cement samples. Results showed an undeniable role of fibres in changing the behaviour of the soil–cement–fibre matrix from brittle to ductile producing post-peak behaviour. The results also show that compressive, tensile and flexural strengths of soil–cement materials improved dramatically by adding steel fibres to the matrix.

Stiffness Degradation and Damping Ratio of Sand-Gravel Mixtures Under Saturated State

Abstract: The aim of this research was to explain the effects of gravel content using the intergrain state concept, relative density and confining pressure on G max, G/G max–γ and D–γ curves and the reference strain (γ r). A total of 45 G–γ and D–γ curves derived from resonant column testing and cyclic triaxial testing along with S-wave velocity measurements obtained using the bender element technique were assessed. The test specimens were prepared with different gravel contents (0, 30, 50, 75 and 100%) under different relative densities (10, 30 and 60%) and mean effective confining pressures (100, 300 and 600 kPa). Comparison of the G max results of the resonant column and bender element tests was also carried out. The desired excitation frequencies and ratios λ/D 50 and d/λ (where λ is wavelength, d is transmission path length and D 50 is average particle size) were determined based on the bender element tests results. The test results were used to evaluate the empirical equation for prediction of G max and to develop a new prediction equation with which to estimate γ r. The results of the tests were used to validate previous models and empirical curves.

Influence of Demolition Waste Fine Particles on the Properties of Recycled Aggregate Masonry Mortar

Abstract: This paper analyses the influence of the fine fraction of two types of construction and demolition waste (CDW1 and CDW2) on the properties of recycled aggregates (RA) and masonry mortars. The CDW1’s main component was ceramic while the CDW2 were concrete. Three different kinds of fine RA were produced from each source of CDW; the first type was produced by only using the fraction finer than 4.76 mm, the second one by employing only the coarser fraction than 4.76 mm, and the third type was a mix of both fractions of CDW. The masonry mortars were produced employing the 100% substitution of natural aggregates. The results show that all the recycled mortars achieved a higher water retentivity capacity than that of the conventional mortars. However, the sole use of the fine fraction of the CDW was found to have a deleterious effect over the hardened mortar properties, thus making it only adequate for the rendering or bonding of interior walls at or above ground level. In contrast a combination of both the fine fraction and coarse fraction of the CDW in the production of the RA achieved all the minimum requirements for rendering and bonding masonry mortar.

Experimental Investigation of Properties of Concrete Containing Recycled Construction Wastes

Abstract: This research focused on investigating the effects of recycled aggregates on the material properties of concrete and the structural performance of reinforced concrete beams. Two different sources of recycled aggregates, crushed red bricks and demolished concrete, collected from local construction and demolition wastes, were analysed. The pre-wetting method was applied to recycled coarse aggregates aiming to study its effects on concrete specimens. Experimental results assisted by regression analysis revealed that the pre-wetting method could minimize the negative effects caused by recycled aggregate itself on the concrete slump and compressive strength test results. Pre-wetting method was also found improving the dynamic modulus of elasticity for concrete specimens. Adding supplementary cementitious materials was not as effective as the pre-wetting method in enhancing concrete slump, ultrasonic pulse velocity (UPV), strength, or dynamic modulus of elasticity. The reduction of concrete UPV and compressive strength caused by recycled aggregates were more significant in the early curing age. Flexural tests on reinforced concrete beams indicated that although adding recycled concrete aggregates did not significantly change the beam failure load, the ultimate deformation of reinforced concrete beams was reduced by displaying more brittle failure behaviour. It was indicated that the failure mode of beam was changed from flexural to shear, inferring that shear capacity of beam with RCA was reduced. Future research directions were proposed focusing on the durability studies of concrete members containing recycled aggregates especially when the pre-wetting method was applied.

Water Permeation Properties of Self Compacting Concrete Made with Coarse and Fine Recycled Concrete Aggregates

Abstract: The paper presents results of an experimental investigation carried out on the water permeation properties of self compacting concrete (SCC) containing fine recycled concrete aggregates (FRCA) and coarse recycled concrete aggregates (CRCA) as replacement of fine natural aggregates (FNA) and coarse natural aggregates (CNA), respectively. The replacement levels of CNA with CRCA were kept as 0, 50 and 100 %. For 50 and 100 % replacement of CNA with CRCA, 0, 25 and 50 % FRCA were used in place of FNA. In all the SCC mixes fly ash was used as partial replacement of Portland cement. Properties of fresh SCC were assessed using slump flow test, V-funnel test and L-box test. The water permeation properties of hardened SCC were investigated using initial surface absorption test, water permeability test and capillary suction test. The compressive strength of all the mixes was also determined. The results indicate that increasing the replacement level of CNA with CRCA has been observed to deteriorate the properties of SCC, whereas the replacement of FNA with FRCA up to 25 % has been found to improve the water permeation properties and compressive strength of SCC mixes up to some extent. Results of this investigation lend support to the use of recycled aggregates in SCC.

Field Tests on Influencing Factors of Negative Skin Friction for Pile Foundations in Collapsible Loess Regions

Abstract: As a reliable building foundation form, piles are driven into collapsible soil layers to ensure stability of foundations. Because of water immersion, significant subsidence occurs on collapsible loess; then negative skin friction emerges on the pile surface, which eventually causes serious bearing capacity failures of pile foundations. Relying on water immersion tests of multiple piles in Lanzhou, China, this study analyzed the influencing factors of negative skin friction for pile foundations in collapsible loess regions. The main factors studied in this research are cumulative relative collapse amount, pile type, and change in loess collapsibility. The results demonstrate that the maximum negative skin friction has a negative correlation to the cumulative relative collapse amount, which is determined by the degree of difficulty of the emergence of the shear fracture surface. Owing to the compaction effect of the driven pile and surcharge load of the exploded pile, their negative skin frictions increase in varying degrees compared to that of the bored concrete pile. At the same test site, the changes in loess collapsibility are mainly affected by natural moisture content and dry density. Increases in both the natural moisture content and dry density reduce the loess collapsibility, immersion settlement rate, and negative skin friction of pile. The loess collapsibility can be improved by surcharge loading and pre-watering to reduce the adverse effect of negative skin friction on pile foundations in engineering applications.

Experimental study and modeling of fiber volume effects on frost resistance of fiber reinforced concrete

Abstract: In the present study, the effectiveness of fiber inclusion on enhancing frost durability was experimentally examined. Polypropylene fiber of 0.2, 0.3, 0.4, and 0.5% and steel fiber of 0.2, 0.4, 0.6, 0.8, and 1.0% by volume fraction were used. Additionally, reference and air-entrained specimens (with 5% air content) were prepared to compare the results. The water/cement ratio for all concrete mixtures was 0.465. The compressive and tensile strengths, and longitudinal strains of frost-exposed specimens were measured. The results showed that both fibers improved the frost resistance of concrete, and 1% steel fiber inclusion caused the samples to be safe against freeze–thaw cycles as well as air entraining. Minimum fiber volumes of 0.4 and 0.5% were required for frost resistance in the steel and polypropylene fiber specimens, respectively. The results were also numerically examined using an artificial neural network (ANN). Data analysis showed that the ANN was capable of generalizing between input and output variables with reasonably fine predictions.

Transition Probability Matrices for Flexible Pavement Deterioration Models with Half-Year Cycle Time

Abstract: Pavement performance models, a vital part of pavement management systems and life-cycle analysis, are generally divided into deterministic and probabilistic ones. Among probabilistic models, the Markov chains are attracting great attention. Transition probability matrices were developed for flexible pavement road network of the Republic of Moldova using the IRI values collected twice a year, in spring and in autumn, from 2013 to 2015. Consequently, a half-year cycle time was established. The aim of this paper is to demonstrate that it is feasible to develop transition probability matrices for an entire flexible pavement network using data from a short data collection period, and simultaneously carrying out maintenance and rehabilitation activities, if some assumptions are made. Results showed that road sections can drop two or three states in one cycle time, not only remaining in the same state or evolving to the next one, as it is usually assumed in pavement performance modeling. These models are proposed for countries in similar circumstances; a network with no new roads constructed in last decades, pavements maintained or rehabilitated in different moments during their service life, invalid or useless pavement condition data from previous years and unknown pavement structure in most of the sections.

Dynamic Properties of Saturated Sands Mixed with Tyre Powders and Tyre Shreds

Abstract: This study examined the effect of adding tyre powders and tyre shreds on the liquefaction potential of loose saturated sandy soil. Also, the dynamic properties of reinforced soil such as the damping ratio and shear modulus were investigated. To this end, a series of 1-g shaking table model tests were carried out at different percentages of sand–tyre powders and sand–tyre shreds mixtures. The results showed that the use of tyre powders and tyre shreds decreases pore-water pressure due to liquefaction. Maximum shear modulus of reinforced soil increased with the increase in tyre powder content in the mixture. However, an increased percentage of tyre shreds had no noticeable effect on maximum shear modulus. Furthermore, the mean damping ratio increases with the increase in tyre powder content in the specimens. Therefore, as the percentage of tyre shreds is increased up to 10%, the mean damping ratio experiences an increasing trend. Nevertheless, at values above 10%, the mean damping ratio reduces. In general, reinforcing soil with tyre powders and tyre shreds reduces the deformations caused by liquefaction.

Structural Health Monitoring-Oriented Finite-Element Model for a Large Transmission Tower

Abstract: To obtain accurate finite-element (FE) models for structural health monitoring (SHM), effective modeling techniques are essential. This paper presents the process for establishing a 131-m large transmission tower’s SHM-oriented FE model. Incorporated procedures are appropriate modeling, manual tuning, model updating, and model validation. Through these works, a detailed realistic model that can reproduce all the experimental dynamic characteristics is obtained, and important conclusions about establishing SHM-oriented FE models for large steel pylon structures can be drawn accordingly: (1) it is necessary to model all the bar members using beam or truss elements of equivalent cross sections for local structural behavior exploration; (2) some components (e.g., ladders, steel plates, and rivets) are no influence on the structural overall stiffness, but their contributions to mass cannot be ignored in modeling; (3) the response surface (RS)-based FE model updating method is effective for complicated pylon models; (4) manual tunings are needed to ensure the quality of model updating.

Effects of Polymeric Coating the Aggregate Surface on Reducing Moisture Sensitivity of Asphalt Mixtures

Abstract: This paper presents the theoretical and experimental concepts of predicting moisture damage in asphalt concrete mixes using the surface free energy (SFE) concept and laboratory dynamic test, respectively. The SFE characteristics of aggregates and asphalt binders have been evaluated using a Universal Sorption Device (USD) and Wilhelmy Plate (WP) methods, respectively. To validate the results of SFE tests, a dynamic modulus test was conducted on the asphalt mixtures in a controlled stress mode under dry and wet conditions. The results of this study show that the polyvinyl chloride (PVC) coating decreases significantly the total SFE and polar SFE, and leads to an increase in the non-polar SFE of the aggregates, which make aggregates be hydrophobic. This occurrence increases the coating ability of aggregates by the asphalt binder. Comparison between the results of dynamic modulus test in dry and wet conditions confirms the results obtained from the SFE method. P index, which is the percentage of the aggregate surface that experiences stripping in different cycles of loading in wet condition, is obtained by the relation between the concepts of two investigated methods in this study.

Centrifuge Model Test on Unsaturated Expansive Soil Slopes with Cyclic Wetting–Drying and Inundation at the Slope Toe

Abstract: The influence of dry unit weight and matric suction on the shear strength and deformation characteristics of unsaturated expansive soil was studied by triaxial tests. Artificial rainfall system and lighting–winding system were, respectively, set up for the unsaturated expansive soil slope centrifuge models to simulate wetting–drying cycles. Three kinds of centrifuge model tests concerning different sequences between centrifuge running and wetting–drying cycles on slope surface and inundation at the slope toe were conducted on the unsaturated expansive soil slope models with two different dry unit weight, water contents and slope ratios. The slope settlement and horizontal displacement, failure mechanism, and cumulated cracks on unsaturated expansive soil slope centrifuge models were investigated and analyzed. It was found that the crack accumulation induced by wetting–drying cycles or softening behavior induced by inundation at the slope toe was crucial to understanding the rainfall-induced progressive failure, which occurred from the slope toe and developed upwards in unsaturated expansive soil slopes. Therefore, cover layer should be built for unsaturated expansive soil slopes from rainfall infiltration into the cracks induced by wetting–drying cycles, and at least enough drainage measures should be taken to reduce water infiltration into the unsaturated soil slope and inundation at the slope toe.

Properties of Drained Shear Strength of Expansive Soil Considering Low Stresses and Its Influencing Factors

Abstract: The shallow failure of most expansive soil slopes undergoing wet–dry cycles occurs during or after long-term rainfall. According to the actual failure state of an expansive soil slope, the conventional direct shear equipment with low normal stresses was used to evaluate the effects of initial dry density, initial moisture content, and number of wet-dry cycle with or without loading on drained shear strength for the compacted expansive soil from Nanning, China. The saturated drained direct shear tests were also performed on the natural expansive soil specimens from Nanning by considering the influence of wet–dry cycles with loading and low normal stresses. Furthermore, consolidated drained triaxial compression tests on compacted specimens were conducted. The test results show that the drained shear strength of expansive soil was primarily affected by the magnitude of normal stresses, and also influenced by the initial moisture content, initial dry density, and number and type of wet–dry cycles. It is more realistic to consider the effect of loading during wet–dry cycles than that without loading. The effective drained shear strength envelopes with low normal stresses were plotted and well fitted by the generalized power function. At low normal stress levels, the drained shear strength still decreased with the increasing number of wet–dry cycles, and the effective cohesion intersects tended to be zero after being subjected to eight wet–dry cycles. This provided a theoretical basis for properly interpreting the shallow failure of expansive soil slopes.

Performance of the Prestressed Composite Lining of a Tunnel: Case Study of the Yellow River Crossing Tunnel

Abstract: This paper presents the performance of a new prestressed composite lining applied in shield tunnels for water conveyance. The Yellow River Crossing Tunnel of the Middle Route Project of the South-to-North Water Division Project is adopted in this study as a case, and a three-dimensional finite element model is established to analyse the stress distribution and deformation feature of the prestressed composite lining when the tunnel is under the assembly condition, the tension condition and the water-filled condition. The finite element model is verified by comparing with the results of the full-scaled simulation experiment. The calculation and analysis results reveal that further open of the segmental joint gaps can be limited and full circumferential compression of the secondary lining can be realized when the tunnel is under the water-filled condition, which are conducive to long-term operation of the prestressed composite lining. The membrane has a significant effect on preventing stresses from being transmitted between the segmental lining and the secondary lining. The numerical calculations are verified by the results of the full-scaled simulation experiment, and the three-dimensional numerical model combined with the analysis method used can simulate the structural characteristics and the bearing mechanism of the prestressed composite lining.

The Efficiency of the Ability of Isolation Piles to Control the Deformation of Tunnels Adjacent to Excavations

Abstract: There is a lack of research on the mechanisms by which isolation piles affect displacements in deep soil layers and the use of isolation piles to control the displacement and deformation of the existing tunnels adjacent to deep excavations. This paper examines a large, deep excavation project in which isolation piles were used to protect a nearby existing tunnel. A finite-element model that considers the small-strain characteristics of the soil was used to simulate this project. After the numerical model is verified, it is used in a parametric analysis of the mechanisms by which isolation piles control the displacement of deep soil layers and the deformation of tunnels near excavations. The results show that isolation piles have both a barrier effect and a traction effect on the surrounding soil and adjacent tunnels. When the traction effect is larger, isolation piles can exacerbate the horizontal displacement of the soil and tunnel within a certain depth range and actually increase tunnel deformation. Burying the isolation piles reduces this traction effect and improves their ability to isolate tunnels from displacement. All else being equal, isolation piles more efficiently control deformation if they are near the tunnel.

Analysis of Negative Skin-Friction on Single Piles by One-Dimensional Consolidation Model Test

Abstract: The computer program pile negative skin friction (PileNSF) was developed by the authors to predict the bearing capacity of a pile embedded in a consolidating ground due to surcharge loading. The program uses a one-dimensional analytical soil-pile model, which was formulated based on the nonlinear load-transfer method and Mikasa’s generalized one-dimensional consolidation theory. To investigate the development of negative skin friction on single piles, as well as to validate the computer program (PileNSF), a laboratory model test was performed in this study. The clay layer was subjected to increasing surcharge loads to simulate actual field conditions. Results showed that as excess pore pressure decreases and as surcharge load increases, the dragload and downdrag on pile increases. The measured values of soil settlement, excess pore water pressure, and axial force on pile were compared with the predicted values obtained from the computer program. The results of the computer program (PileNSF) showed to be in good agreement with the measured data. Therefore, negative skin friction on single piles can be effectively predicted using the computer program, PileNSF, provided that reasonable parameters are used in the analysis. After validating the program, a parametric study was carried out to study the influence of various pile design parameters on negative skin friction.

Utilization of Natural and Waste Pozzolans as an Alternative Resource of Geopolymer Mortar

Abstract: The objective of this research was to investigate the engineering properties and mix design of geopolymer mortar made using fly ash, natural zeolite and ground granulated blast furnace slag as source material and combination of sodium hydroxide and sodium silicate as alkaline activator. To study the effect of sodium hydroxide concentration on compressive strength, three different sodium hydroxide solutions (8, 10 and 12 M) were used. The ratio of sodium silicate/sodium hydroxide was varied from 1.0, 2.0 to 3.0. The test results demonstrate that the compressive strength of developed geopolymer mortar increases with increase in the concentration of sodium hydroxide solution and sodium silicate content in the activator. The average maximum compressive strength was obtained when the sodium hydroxide concentration was 12 M and sodium silicate content was 3.0. At higher alkali content, the water absorption is less due to lower void spaces. The utilization of industrial waste materials such as fly ash, ground granulated blast furnace slag and natural pozzolans such as zeolite would lead to significant economic and environmental benefits in geopolymer production.

Experimental Study of Reinforced Concrete T-Beams Strengthened with a Composite of Prestressed Steel Wire Ropes Embedded in Polyurethane Cement (PSWR–PUC)

Abstract: This paper presents the experimental response of reinforced concrete T-beams strengthened with an innovative technique, namely, a composite of prestressed steel wire ropes (PSWRs) embedded in polyurethane cement (PSWR–PUC). The flexural behaviour of the PSWR–PUC-strengthened beams was investigated. One control beam, three PSWR-strengthened beams and five PSWR–PUC-strengthened beams were constructed and tested under four-point bending. The experimental variables included the material into which the wire rope is embedded, the thickness of the PUC, the number of wire ropes, the loading method and the wire rope anchoring type. The test results indicated that relative to PSWR-strengthened beams, PSWR–PUC-strengthened beams had significantly greater yield load, ultimate load and stiffness at the service load, and these enhancements increased significantly with increasing PUC thickness. Relative to using polymer mortar for PSWR strengthening, using PUC increased the durability of the steel wire ropes in the PSWR–PUC-strengthened composite. The cracking load of the PSWR–PUC-strengthened composite mainly depended on the prestressing effect of the wire ropes. However, after cracking, crack constraint in the PSWR–PUC-strengthened beam was dependent on the crack-suppression effect of PUC, especially during the later cracking stage. PSWR–PUC strengthening can effectively ensure secure anchoring by reducing the number of steel wire ropes required. These results indicate that PSWR–PUC strengthening has potential as an external strengthening technique for concrete structures.

Durability of CFRP-Wrapped Concrete Exposed to Hydrothermal Environment

Abstract: In recent years, it has become increasingly common to strengthen concrete by wrapping carbon fibre reinforced polymer (CFRP) laminates to improve its compressive strength and ductility. However, studies on the durability of CFRP-confined concrete are relatively scarce, which could significantly hinder the application of CFRP in structural reinforcement. An experimental study was conducted to investigate the effect of exposure to natural hydrothermal environment on the confinement system of CFRP-wrapped concrete in this study. Three kinds of specimens were prepared and tested after natural exposure to the subtropical environment in South China, including 35 CFRP flat coupons, 35 epoxy adhesive flat coupons and 60 CFRP-wrapped concrete cylinders. The test parameters included the exposure duration (0, 6, 12, 18 and 30 months) for all specimens and the number of CFRP layers (0, 1, 2 and 3) for the CFRP-wrapped concrete specimens. Based on the experimental results, a compressive strength model for the CFRP-confined concrete exposed to hydrothermal environment was proposed. The results show that hydrothermal environment had a significant effect on the mechanical properties of the epoxy adhesive, but a relatively slight effect on that of the CFRP. Due to the deterioration of the CFRP, the compressive strength of CFRP-wrapped concrete gradually decreased with the increase of exposure duration. After a 30-month exposure, the compressive strength of CFRP-wrapped concrete has a decrease of approximately 10%.

Seismic Assessment of a School Building in Nepal and Analysis of Retrofitting Solutions

Abstract: Recent earthquakes highlighted the vulnerability of some infilled reinforced concrete structures due to the presence and distribution of the infill masonry walls. Buildings such as school buildings and residential buildings are typically not designed considering the contribution of the infill panels to the structure strength and stiffness, when these are subjected to earthquakes. The lack of consideration of the infill panel results in observed poor performance and structural collapses. This manuscript presents a numerical study of a school in Nepal, representative of those existent in the country. Non-linear numerical analyses were carried out to assess the seismic vulnerability in terms of peak inter-storey drifts. In addition, results will be presented and discussed in terms of peak inter-storey drift profiles and peak base shear. Results from a seismic vulnerability assessment of the pre-earthquake structure indicate that the presence of the infill panels in the original structures were responsible for the development a soft-storey mechanism, combined with torsion. Following the seismic vulnerability assessment, four different retrofit solutions were tested and compared with the results of the original structure to gain an understanding on the structural efficiency of each proposed solution. The retrofit solutions proposed revealed to be efficient and reduce the seismic vulnerability. The retrofit solution showing best results correspond to the ones in which reinforced concrete column jacketing was employed.

Effects of High Temperature on Mechanical Properties of Polyvinyl Alcohol Engineered Cementitious Composites (PVA-ECC)

Abstract: The influence of elevated temperatures on the mechanical properties of polyvinyl alcohol engineered cementitious composites (PVA-ECCs) was investigated in this study. A comparison of the compressive strength, flexural strength, compressive strain capacity, and modulus of elasticity of specimens with/without PVA fiber (volume dosage of PVA fiber: 2%) was conducted. The microstructure of PVA-ECC exposed to different high temperatures was studied using scanning electron microscopy (SEM). Based on previous thermal analysis tests of PVA fibers, all specimens were subjected to 20, 100, 200, 300, and 400 °C for 6 h. The experimental results showed that the compressive strength, flexural strength, and modulus of elasticity decreased as the temperature increased, whereas the compressive strain capacity increased with temperature. PVA incorporation significantly increased the flexural strength initially but accelerated the rate of strength reduction at high temperatures. The investigation of the PVA-ECC microstructure provides a fundamental reason for the decrease in the macro-mechanical properties. These findings provide guidance for the engineering applications of PVA-ECC to resist high temperatures.