Publications

Statistical models for mechanical properties of UHPC using response surface methodology

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

Steel Moment-Resisting Frame Reliability via the Interval Analysis by FCM-PSO Approach considering Various Uncertainties

One important issue in compiling siesmic fragility curves is blending and incorporating uncertainties into the model under seismic conditions. Methods used in this regard are either approximate, costly and time-consuming. To address this, the optimized fuzzy method is used. To compile the fragility curve, epistemic and aleatory uncertainties have been incorporated in which model parameters are fuzzy values and FCM-PSO method is used to estimate mean and standard deviation of fragility curve. The FCM-PSO algorithm is trained using scenarios compiled via the IDA method. Results obtained from the full Monte Carlo method were used for verification. The method employed here is advantageous with regard to both accuracy and execution time.

Cement mixtures containing copper tailings as an additive: durability properties

The effects of copper tailings as an additive, on some durability properties of cement mixtures were investigated. In each mixture, copper tailings addition levels by mass were 0%, 5% and 10%. Compared to the control samples, copper tailings blended pastes showed superior performance against autoclave expansion while insignificant decreases in sulfate resistance of mortars were observed. Copper tailings increased the water absorption and total permeable voids of concretes slightly. However, the compressive and flexural strengths of blended concretes were higher than those of the control samples. Similarly, improved resistance to acid attack and chloride penetration as the copper tailings content of concretes increased were also observed. Results further showed that the ASTM C 1202 rapid chloride permeability test may not be a valid indicator of chloride migration in mixtures containing conductive copper tailings. These results suggest that copper tailings can potentially enhance the durability properties of cement based materials.

Seismic behaviour of the old-type gravity load designed deteriorated RC buildings in Cyprus

Natural Building Cut Stones of North Cyprus: Meluşa and Karpaz Stones

No abstract is provided for this article.

Seismic Performance Assessment of Semi Active Tuned Mass Damper in an MRF Steel Building Including Nonlinear Soil–Pile–Structure Interaction

CO₂-full factorial optimization of an ultra-high performance concrete mix design

This article presents a factorial modelling, as well as an optimization, of the mix proportion of ultra-high performance concrete (UHPC) in terms of maximising the 28-day strength and minimising CO2 emissions. A full factorial design and desirability function optimization method were performed to find the best UHPC ingredient proportions. To improve the concrete properties, the concrete performance in terms of CO2 emissions and environment effects should be considered. Ultra-high performance with superior properties requires a large amount of cement, steel fibre and an admixture; however, from an environmental perspective, cement and admixtures and steel fibre are the important matter for global warming as cement production corresponds to 5% of all the CO2 emissions around the world. In addition, the 28-day compressive strength is one of the most important properties of concrete and is related to other mechanical properties; therefore, the 28-day compressive strength and carbon oxide emissions were selected as the responses to produce the green UHPC with high performance. The mix design parameters were the cement content (C), the steel fibre amount (F), the superplasticiser (SP), the silica fume amount (SF) and the water to cementitious ratio (W/C). The variables were compared by fine aggregate mass. The optimized ingredient mix designs are valid for the mixes with .18–.32 W/C ratio, .04–.08 steel fibre, .7–1.3 cement, .15–.30 silica fume, and .04–.08 superplasticiser by fine aggregate mass.

Ridge Regression Analysis Application on Iterative FR-SCC Mix Design to Predict Compressive Strength and Slump Flow Parameters

SELIMIYE MOSQUE IN NICOSIA

Effects of crushed stone dust on some properties of concrete

Crusher dust is a fine material formed during the process of comminution of rock into crushed stone or crushed sand. This dust is composed by particles which pass 75 μm BS sieve. Effects of dust content in aggregate on properties of fresh and hardened concrete are not known very well. An experimental study was undertaken to find out the effects of various proportions of dust content on properties of fresh concrete and hardened concrete.

Effect of Corrosion Damage on the Performance Level of a 25-Year-Old Reinforced Concrete Building

Corrosion is a long-term process resulting in the deterioration of the reinforced concrete (RC) structures. Most of the structural problems observed under the impact of either earthquakes or service loads might occur due to corrosion. Therefore, prediction of the remaining service life of a corroding RC structure plays an important role to prevent serious premature damage. In this study, a corroded, 25-year-old high school building which has been demolished at an earlier time was analyzed as a function of corrosion rate. Bond-slip relationships were taken into account in nonlinear analyses as a function of corrosion rate for different time periods (i.e., non-corroded (t: 0), existing (t: 25) and 50 years after construction); and they were used to ensure the effect of time-dependent slip rotation on the global structural behaviour by modifying the target post-yield stiffness of each structural member. Nonlinear push-over analyses were performed by defining the time-dependent plastic hinge properties as a consequence of corrosion effects. In order to define the performance levels of three different time periods, nonlinear incremental dynamic analyses (IDA) were performed for 20 earthquake ground motion records as a function of corrosion rate. Results showed that bond-slip relationship between concrete and steel is very important in evaluating the non-linear behaviour of corroded RC structures.

Time-dependent seismic performance assessment of a single-degree-of-freedom frame subject to corrosion

Corrosion of reinforcement bars in concrete is directly responsible for serious damage to concrete structures, which may result in premature failure of the structures as a function of time. Therefore, it is necessary to evaluate its damage on the structural performance level. Many models have been developed to predict the corrosion rate of steel in concrete and its effects on structures. It is also possible to evaluate and identify the seismic performance level of reinforced concrete (RC) structures. This study contributes to an understanding of the relationship between these two topics as a function of time to predict the performance level of corroded RC buildings. Three combined parameters (loss of the cross sectional area of reinforcement bars, reduction of the concrete strength, and additional displacement due to slip) as a consequence of corrosion effects were calculated as a function of the corrosion rate for five different time periods (i.e., non-corroded (t: 0), 25, 50, 75, and 100 years). Obtained results were used to perform nonlinear time-history analyses for 20 ground motion records. The results showed that the effect of the corrosion of steel on the seismic performance level is highly significant, and it should be considered carefully in performance analysis.

Some mechanical properties of normal and recycled aggregate concretes

This paper describes an experimental study conducted to investigate the properties of concretes produced with recycled aggregates and normal aggregates for two different concrete classes (C20/25, C30/37). Tests of compressive strength, splitting tensile strength, ultrasonic pulse velocity, rebound hammer, wet and dry density and freeze-thaw resistance were conducted on specimens of the concretes. Moreover slump test was conducted on fresh concrete. The results showed that the slump of recycled aggregate concrete (RAC) was less than that of normal aggregate concrete (NAC). For class C20/25, the average compressive strength, rebound hammer and density of the RAC were 26%, 17% and 16.6% less, respectively, than those of NAC. The splitting tensile strength of RAC was 3.5% greater that of NAC. Moreover for C30/37 the average compressive strength, splitting tensile strength, rebound hammer and density of the RAC were 32.5%, 12%, 21% and30% less, respectively, than those of NAC. For class C20/25 and class C30/37 the ultrasonic pulse velocity of RAC was 17% and 18% smaller than that of NAC, respectively. RAC for C20/25 lost 2.5% more weight than NAC in freeze-thaw resistance tests and RAC for C30/37 lost 29% more weight than NAC in this test.

Rheology, strength and durability properties of mortars containing copper tailings as a cement replacement material

This paper investigates the suitability of copper tailings as a cement replacement material in mortars. The impact of copper tailings at 0%, 5%, 10% and 15% cement replacement level by mass on the rheology, mechanical and durability properties of mortars was evaluated. Results revealed higher yield stress and flow loss in mixtures incorporating copper tailings. High mortar compressive strength, flexural strength and abrasion resistance were determined at 5% cement replacement level. Furthermore, despite increased rate of water absorption, higher resistance to acid attack and chloride penetrations were also observed in samples containing copper tailings. These improved properties were more pronounced in samples containing pre-wetted tailings at 5% cement substitution level. The use of copper tailings in mortars could bring about significant environmental conservation and sustainability gains.

Using Recyclable Steel Material in Tall Buildings

Physical and durability properties of recycled polyethylene terephthalate (PET) fibre reinforced concrete

Utilisation of recycled Polyethylene Terephthalate (PET) waste in construction materials contributes towards the environmental sustainability by reducing the accumulation of non-degradable waste into the nature. This study aims to contribute to the knowledge about the material behaviour of recycled PET fibre reinforced concrete (RPFRC). The present work investigates the influence of recycled PET fibres on the physical properties of concrete, with a focus on the durability, acoustic properties, and the mechanical response to heat exposure. Mixtures with varying fibre dimensions and fibre volumes were prepared. Fibre addition reduced the bulk density, increased the permeable void volume, and decreased the ultrasonic pulse velocity (UPV) of concrete, suggesting possible porosity formations within. Water permeability of RPFRC samples was substantially higher than the concrete without fibres and the findings were in agreement with rapid chloride permeability test results. Sound permeability was slightly reduced by fibre addition. RPFRC samples were heated at three different temperatures and tested for compressive and flexural strengths. At room temperature, fibre addition caused negligible variations in compressive strength but notable increase in flexural strength. Strength values were reduced slightly with fibre addition when samples were exposed to 100 °C and 200 °C, indicating possible response of PET fibres to high-temperature exposure.

Seismic performance evaluation of corroded reinforced concrete structures by using default and user defined plastic hinge properties

The primary objectives of this study was to investigate the effects of default hinge properties based on FEMA-356 (FEMA-356, 2000) and user-defined hinge properties on the timedependent seismic performance levels of corroded RC buildings. An assumed corrosion rate was used to predict the capacity curve of the buildings by using default and user-defined plastic hinge properties as a function of time (t: 25 years, and t: 50 years). Two, four and seven stories of RC buildings were considered to represent the effects of default and user- defined hinge properties on story levels. For the modelling of user-defined hinge properties, the time-dependent moment-curvature relationships of structural members were predicted as a function of corrosion rate for two different time periods in order to perform push-over analyses, while default hinge properties were used for the other case based on the ready documents by FEMA-356 (FEMA-356, 2000). Then, the nonlinear time-history analyses for both corroded and non-corroded buildings were performed by using 20 individual earthquake motion records. Seismic performance levels of non-corroded buildings and predicted time-dependent seismic performance levels of corroded buildings were compared based on their story levels as a result of user-defined and default hinge properties. Limit–states at each performance levels (e.i. immediate occupancy, life safety, collapse prevention and collapse) were obtained. The obtained results were summarized to compare the differences in the results of seismic response of the buildings due to user-defined and default hinge properties for both corroded and non-corroded cases.

Seismic Behavior and Damping Efficiency of Reinforced Rubberized Concrete Jacketing

Over the last few years, many studies were performed to investigate rubberized concrete’s behavior as a sustainable alternative for conventional concrete by replacing natural aggregates with recycling old rubber tires. These studies have shown that the concrete's mechanical and durability properties are significantly reduced, while its ductility and damping ratio improved. Accordingly, using this material in RC structures could be a promising solution for improving their energy dissipation capabilities. Currently, the literature lacks a numerical study that can highlight the effectiveness of using high-strength rubberized concrete for retrofitting RC structures subject to earthquake loadings . Therefore, this research investigates the seismic performance of reinforced concrete buildings strengthened using different high-strength rubberized concrete mixtures under various ground motion excitations. As a part of the study, finite element models of reinforced concrete structure retrofitted with these concrete mixes will be analyzed using nonlinear response history analysis and compared against two different control models composed of a bare structure and a jacketed RC structure using the control concrete mixture. In general, using rubberized concrete jacketing improved the seismic performance of the bare structure significantly. Furthermore, utilizing high-strength rubberized concrete rather than the control one resulted in increasing the damping energy and slightly reducing the base shear forces of the structure.