Destructive tests for evaluating concrete compressive strength are costly and challenging in certain instances. Using a rebound hammer (RH) and ultrasonic pulse velocity (UPV), i.e., non-destructive methods for strength evaluation, proved more beneficial in all senses. However, calibrating the model between non-destructive testing (NDT) and compressive strength is essential for estimating strength. The reliability of this calibration is a crucial task that leads to selecting a minimal number of cores to be taken out (core) from a structure. The present study aims to identify and optimize the on-site reliability model. Extensive data from 275 core samples were obtained from the Construction Diagnostic Centre, Pune (India), which RH and UPV examined. The cores are taken from thirty existing RCC structures built between 1975 and 2005. The Root Mean Square Error (RMSE) and the coefficient of determination (R2) for single method (SM) and combined method (CM) are used to investigate the total number of cores needed for calibration. According to RMSEpred and R2pred, at least 6–8 cores are required to achieve the correct prediction phase with a CM rather than using SM. The CM leads to more reliable results than an SM with the least RMSE and higher R2 values by analyzing 100 iterations for each number of cores (NC). Also, the CM shows more reliable results than the SM in the fitting and prediction phase. As a reasonable number of samples, 9 cores must be considered to converge for an SM, compared to 6–8 cores necessary for CM to estimate the strength precisely.

This study highlights the utilization of additives in superplasticizers, fly ash, polypropylene fibers, and carbon steel fibers to achieve the designed fresh and mechanical characteristics of Self-compacting concrete (SCC) while considering environmental sustainability. This study employs Taguchi's L18 design methodology to investigate the impact of the additives with varying levels on the rheological and mechanical properties of SCC. The research assesses both fresh properties (slump flow, V-funnel, J-ring) and hardened properties (split tensile and compressive strength at 7 and 28 days) of self-compacting concrete. Apart from conventional tests, microstructural analysis of fly ash and designed mixes are also performed wherein X-ray diffraction is utilized to classify fly ash, SEM is utilized to get microscopic insights into the arrangement and interaction of components, and EDS is utilized to quantify the elemental composition. This two-tiered approach enables a thorough grasp of the impact of regulating materials on both the macro properties and microstructure of SCC. Further, multiple regression analysis develops a predictive model using experimental data to understand how these components influence SCC characteristics. Notably, the study reveals that fibers have a detrimental effect on SCC flow properties but a beneficial impact on hardened concrete properties. Likewise, the influence of superplasticizers outweighs that of fly ash in shaping SCC properties. Remarkably, microstructural insights align with the predictive model, highlighting the dominance of superplasticizers over fly ash. This holistic methodology bridges the gap between material composition, macro behavior, and microstructure, enriching our comprehension of SCC. It offers a robust foundation for enhancing SCC's performance across applications.

The assessment of in-situ structural concrete strength by the core test is expensive, also it needs to validate the correlation between destructive and non-destructive strength of concrete. Reliability of this calibration is a crucial task that leads to the selection of a minimal number of cores. The objective of the present study is to identify and optimize the on-site reliability model. The data is used individually and combined were collected from the Construction Diagnostic Center, Pune, which has tested 30 existing RC structures constructed between 1975 to 2005. A comprehensive data analysis of 275 core samples tested using Rebound number, Ultrasonic pulse velocity has considered for this study. Statistical analysis allows the quantitative evaluation of the cores used for calibration and NDT methods. The findings are based on a broad dataset to enhance the relevance of prediction models, it useful in the estimation of concrete strength of existing structures.

The reliability of the result significantly affects the use of the Coefficient of Variation (within the test variation), which reflects the variability of the concrete properties rather than the standard deviation. For the estimation of reliability and precision, comprehensive statistical analysis (within test variation) is conducted on 534 test samples using a rebound hammer. Different standards, like BIS, EN, ACI, and ASTM, are used in this study to compare the test results. Empirical research revealed that there are contradictions in literature as well as the standards used in many countries. The present paper focuses on detailed investigations of uncertainty measurements of the surface hardness test by statistical parameters (range of rebound index, standard deviation, and Coefficient of Variation). The unbiased estimate of the variability parameters from the published results has been verified concerning to the European standard. Concrete parameters namely cement type, water to cement ratio, compaction deficiency, curing condition, and elevated temperature have an impact on the output of the rebound hardness in terms of the variability of the compressive strength. Based on the results, the authors are willing to propose amendments to the Indian code graciously in compliance with the variability of the rebound hammer.

It is a known fact that the concrete strength is not only affected by the ingredients present in it, but also by the other factors like types of cement used, compaction deficiency, curing condition, elevated temperature, and different w/c ratios. The influence on the rebound hammer has been illustrated in this paper concerning the hardness of the concrete specimens. The effect of cement types, compacting deficiency, w/c ratio, curing condition, and elevated temperature on concrete compressive strength and rebound hardness has been considered for the analysis. From an experimental study, it is found that the reduction of the compressive strength of concrete is between 6 to 41 percent due to insufficient compaction alone when tested using a destructive method. However, the rebound hammer results revealed that there is no reduction in the rebound index. The rebound hardness test cannot predict the compressive strength due to inadequate curing. It is also reported that the rebound index is significantly reduced, with the destructive strength of the concrete specimens. The study revealed that in the case of M30 and M40 grades of concrete, the percentage reduction of the average rebound index is almost higher in all the cases than the average compressive strength at a temperature ranging from 200°C to 800°C. The strength (rebound hardness) measured is either under or overestimated if no attention has been given to different influencing factors. Thus, a reliable and accurate evaluation of strength cannot be guarantee.

Non-destructive testing (NDT) has a vital role in finding surface hardness of concrete members. B-Proceq curve can calculate the concrete strength by providing statistical correlations between the destructive and the non-destructive strength. The regression curve based on the laboratory test may be valid within their implementation boundaries. It is not feasible to extend the validity of these curves to the in-situ test. Factors influencing such curves include the w/c ratio, carbonation effect, exposure to fire, compaction, curing condition, and type of the cement used in concrete, etc. More than 65 years of research data with the Schmidt rebound hammer is used for evaluation. The Authors also addressed the effect of each influencing factor on the performance of the rebound hammer and suggested amendment in the B-Proceq curve. Various factors affect the rebound index significantly and hence their consideration while conducting a rebound test is necessary. The large deviation of curves raised a crucial question of whether the rebound hammer is effective or not in estimating the concrete strength.

Ultrasonic Pulse Velocity (UPV) and Rebound Hammer (RH) are continually adopted methods by the researchers to assess the characteristics and to estimate the compressive strength of the concrete. As matrix of concrete is very complex, it’s obvious that the strength of concrete can be influenced due to even minor change in any of the factor. The factors that influenced the strength of concrete largely are the type and size of aggregates, cement content, physical and mechanical factors. To evaluate the compressive strength considering these factors with higher precision, UPV and RH methods are combined henceforth called SonReb. The results of testing of on-site casted cube samples and cores samples taken from the existing buildings in Pune, India are presented here. The application of the regression model to observe destructive and non-destructive testing were used through SonReb method to evaluate the reliability of concrete. Equations are obtained using multiple regression statistical analysis (MRSA) to access concrete compressive strength and the accuracy of the strength prediction technique is discussed in this paper. The regression curve of proposed model strongly consistent with the models suggested by Meynink, Ramyar et al. and Khedar et.al. It is also concluded that the results obtained from core are underestimate, which reflects the age factor when compared with the samples tested in laboratory. It is also seen that the regression coefficient of both the formulation are closely matching, which indicates no effect of age of samples tested. SonReb results seems to be more accurate and reliable than any individual test performed on the same samples.

Partial replacement of cement with crushed burnt clay brick waste powder (CBP) could reduce CO2 emission, enhance the conservation of natural resources, and decrease the cost of waste disposal sites. The aim of this study is to investigate the use of CBP as a partial replacement for cement in the production of cement mortar. Clinker was replaced by CBP in different proportions (0, 5, 10, 15, and 20%) by weight for cement. The physicochemical properties of cement at the anhydrous state and the hydrated state thus compressive strengths after 7, 28, and 90 days for the mortar were studied. Thermogravimetry analysis (TGA), Differential thermal analysis (DTA) and Thermogravimetry (TG) tests were conducted to investigate the development of cement hydration reactions in the presence of these wastes. Particle size distributions were obtained from laser granulometry (LG) of CBP and cement used in this study. Considering the proportions levels studied, the results indicated that the use of CBP in mixture accelerated the hydration reactions, and there was an indication of pozzolanic activity, particles packing density and compressive strength were maintained. Compressive strength decreased as the replacement level and average particle size increased. The CBP mixture at 20% level had similar or even higher mechanical properties than controlled mortar.

There are many catastrophic effects of an earthquake on a structure. So it is essential to consider earthquake forces on a structure while its designing phase. The major effect on a structure is at joints, so we have to strengthen the joints of a structure. There are various methods available for computation of earthquake such as response spectrum method and time history method. In response spectrum method peak or steady-state responses are plotted to specified load function for all degrees of freedom. This paper highlights different methods used for seismic analysis and their limitations. A case study of Gujarat earthquake is also presented with the effects on various structures.

The process of soil stabilization helps to achieve the required properties in a soil needed for the construction work. The attempt had been made to investigate the effect of lime sludge obtained from paper mill as waste on the strength and compaction of sandy soil with plasticity. The basic properties of soil like liquid limit, plastic limit, shear strength and MDD & OMC were determined before and after addition of lime sludge. The lime sludge was added at 3%, 6% and 9% by weight of soil and mixed with soil at optimum moisture content. The direct shear and compaction tests were conducted without curing of the specimens. It was observed that addition of lime sludge in sandy soil improves the shear strength.

The main aim of using seismic base isolation tool is to reduce the inert ia forces introduced in the structure due to earthquake by shifting the fundamental period of the structure out of dangerous resonance range and concentration of the deformation demand at the isolation system. In the paper a parametric study on Reinforced Concrete (RC) build ing with fixed and isolated base with rubber bearing (RB) and friction isolator (FI) are carried out using response spectrum method. Here, the design spectra recommended by Indian Standard Code IS 1893-2002 (part -I) and Euro Code 8 are considered for comparison. The main objective of this study is to investigate the differences caused by the use of different codes in the dynamic analysis of multistoried RC build ing along with fixed and isolated base condition. Two different floor p lans that are symmetric (SB) and unsymmetric (UB) with torsional irregularity are taken as sample build ing. To evaluate the seismic response of the buildings, elastic analysis is performed using the computer program SAP2000. It is observed from the comparative study that the building response with isolated base is very less to that of building with fixed base in all the cases and IS code depict higher values in all the cases with and without isolation, when compared to that of Euro code.

In this work, a parametric study on reinforced concrete (RC) structural walls and moment resisting frames building representative of structural types using response spectrum method is carried out. Here, the design spectra recommended by Indian Standard Code [1] and two other well known codes (Uniform Building Code, Euro Code 8) have been considered for comparison. The main objective of this study is to investigate the differences caused by the use of different codes in the dynamic analysis of multistoried RC building. Three different floor plans that are symmetric (SB), monosymmetric (MB), and unsymmetric (UB) with torsional irregularity are taken as sample buildings. To evaluate the seismic response of the buildings, elastic analysis was performed by using response spectrum method using the computer program SAP2000. Periods, base shears, lateral displacement and interstory drift, torque located at code defined ground type are comparatively presented. It is observed from the comparative study that the base shear using IS code is higher in all the three buildings, when compared to that of with other codes.

Structural response behavior of Tension Leg Platforms (TLPs) used in deep sea oil exploration is nonlinear due to large displacements and fluid‐structure interaction. Their relative insensitivity in deep sea and excellent station keeping characteristics make them suitable for deep waters, apart from being cost‐effective. This study investigates response behavior of TLP with triangular geometry using Dynamic Morison equation; nonlinearities associated with vortex shedding effects are considered in contrast to the standard Morison equation that has undesirable features in this respect. Numerical studies conducted on TLPs under regular waves with varying hydrodynamic coefficients show that the coupled responses in active degrees‐of‐freedom namely surge, heave and pitch response obtained using Dynamic Morison equation are lesser in comparison to those obtained using standard Morison equation.

Tension leg platforms (TLPs) are compliant-type offshore structures generally used for deepwater oil/gas exploration. Dynamic analysis of three triangular TLP models under regular waves is presented, considering the coupling between various degrees of freedom. The analysis considers various nonlinearities developed due to change in tether tension, change in buoyancy, and hydrodynamic drag force. The hydrodynamic characteristics of the wave loading on the structure are computed using Airy's wave theory and Stokes' fifth-order theory. The hydrodynamic coefficients C-d and C-m vary along the water depth. The low frequency drift response and the high frequency springing response are not considered in the present study. The equation of motion has been solved in time domain using Newmark's integration scheme. Numerical studies are conducted to compare the coupled response of triangular TLPs under regular waves using Airy's wave theory evaluated with Chakrabarti's modification and that obtained by using Stokes' fifth-order nonlinear wave theory. Results show that the coupled response in surge and pitch degree of freedom obtained using Stokes' theory is lesser than that obtained using the Airy's theory. Additionally, the presence of current in the wave field increases the responses in all degrees of freedom in all the cases taken for the study.

Compliant offshore TLPs are essentially meant for deep oil/gas exploration and are usually constructed on the seashore and then towed down to the particular location for anchorage. They are connected to the sea bed by means of pretension cables. The increased use of TLPs in deep waters and necessity of reduction of usually high value of pretension make the effect of variable tension in the tether dynamics more significant. This work presents the dynamic analysis of tethers and TLPs considering the linearly varying tension along the tether length. The modal analysis considers a linear cable equation for tether modeling subjected to tension which varies along its length. A Mathieu stability analysis is then performed for TLPs of different shapes and different water depth vis-à-vis of 527.8, 872, and 1200m respectively to obtain the amplitudes of tether vibrations. The unstable modes of vibration are also verified. The resultant modal forms for the tether's dynamic model are then obtained in form of Bessel's function. From the numerical studies conducted it is seen that increased tether tension not only leads to a stable platform but also improves the stability due to increased hydrodynamic loading contributing to added mass. From the studies conducted it is also seen that the triangular configuration TLPs with increased initial pretension are more stable compared to four leg TLP in the first mode of vibration.

Oil and gas production from deep-water offshore fields represent a major structural engineering challenge for the industry. The tension leg platform (TLP) is a well-established concept for deep-water oil exploration. It is necessary to design an offshore TLP such that it can respond to moderate environmental loads without damage, and is capable of resisting severe environmental loads without seriously endangering the occupants. Seismic analysis of triangular TLP under moderate regular waves is investigated. The analysis considers nonlinearities due to the change in tether tension and nonlinear hydrodynamic drag forces. The coupled response of TLP under moderate regular sea waves due to change in initial pretension in the tethers caused by seismic forces (vertical direction) is then investigated. Seismic forces are imposed at the bottom of each tether as axial forces. The tether tension becomes unbalanced when the hull is under offset position. The vertical component of seismic force is an important item to take into consideration, because it is directly superposed to pretension of tethers. The change in initial pretension due to the vertical component of the earthquake affects the response of the triangular TLP in degrees-of-freedom experiencing such forces. The tether tension varies nonlinearly when the platform is subjected to seismic forces caused by the El Centro earthquake and artificially generated earthquake using Kanai–Tajimi's power spectrum. The response due to earthquakes varies with the intensity of the input ground motion. The seismic response of the triangular TLP exhibits nonlinear behavior in the presence of waves and it is non-proportionately influenced by the wave period and the wave height.

Triangular configuration tension leg platforms (TLPs) are used for deep-water oil/gas exploration. The mechanics of TLP is highly nonlinear due to larger structural displacements and fluid motion–structure interaction. Triangular TLP has major consideration for deep-water application also due to its relative insensitivity with increasing water depth, excellent station keeping characteristics, etc. which makes this as a most cost effective and practical production system for deep waters. This study focuses on the influence of hydrodynamic drag coefficient (Cd) and hydrodynamic inertia coefficient (Cm) on the nonlinear response behavior of triangular TLP models under regular waves. Two typical triangular TLP models vis-à-vis TLP1 and TLP2 are taken for the study at 600 and 1200 m water depths, respectively. Hydrodynamic forces on these TLPs are evaluated using modified Morison equation under regular waves. Diffraction effects are neglected. Various nonlinearities arising due to relative velocity term in drag force, change in tether tension due to TLP movement, and set down effect are being considered in the analysis. The dynamic equation of motion has been solved in time-domain by employing Newmark’s β numerical integration technique. Based on the numerical study conducted, it is seen that the response evaluated using varying hydrodynamic coefficients through the water depth is significantly lesser in comparison to the response with constant coefficients in all activated degrees-of-freedom. However, sway, roll, and yaw degrees-of-freedom are not present due to the unidirectional wave loading considered for the study. The influence of hydrodynamic coefficients in wave period of 15 s is more in comparison with that of 10 s, and is nonlinear. The hydrodynamic coefficients also influence the plan dimension of TLP and its site location (geometry). Therefore, it may become essential to estimate the range of Cd–Cm values to vary through the water depth, based on Reynolds number (Re) or Keulegan–Carpenter number (Kc) even before the preliminary design of the TLP geometry.