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Acceleration-based sensors are widely used in indicating the severity of damage caused to structural buildings during dynamic events. The force rate of change is of interest when investigating the effect of seismic waves on structural elements, and hence the calculation of the jerk is necessary. For most sensors, the technique used for measuring the jerk (m/s3) is based on differentiating the time–acceleration signal. However, this technique is prone to errors especially in small amplitude and low frequency signals, and is deemed not suitable when online feedback is required. Here, we show that direct measurement of the jerk can be achieved using a metal cantilever and a gyroscope. In addition, we focus on the development of the jerk sensor for seismic vibrations. The adopted methodology optimized the dimensions of an austenitic stainless steel cantilever and enhanced the performance in terms of sensitivity and the jerk measurable range. We found, after several analytical and FE analyses, that an L-35 cantilever model with dimensions 35 × 20 × 0.5 (mm3) and a natural frequency of 139 (Hz) has a remarkable performance for seismic measurements. Our theoretical and experimental results show that the L-35 jerk sensor has a constant sensitivity value of 0.05 ((deg/s)/(G/s)) with ±2% error in the seismic frequency bandwidth of 0.1~40 (Hz) and for amplitudes in between 0.1 and 2 (G). Furthermore, the theoretical and experimental calibration curves show linear trends with a high correlation factor of 0.99 and 0.98, respectively. These findings demonstrate the enhanced sensitivity of the jerk sensor, which surpasses previously reported sensitivities in the literature.

Cold joint is one of concreting problem due to delay of casting the second layer. This is due to glitch of one of mechanical machines such as the concrete mixer, concrete truck, concrete batching plants, concrete pumps, and concrete mobile; that cause the stopping of the casting process which produce forced separator. Forced separation is different from known separators like: construction joint, expansion joint and settlement joint, where its location event and shape cannot be determined moreover the design engineer cannot put that in mind during the design phase of building construction. Therefore, the target in this work is to study the effect of delay in time period when casting the second layer of concrete after 4, 9, and 16 hour for two types of concrete with compressive strength 250 kg/cm 2 and 300 kg/cm 2. Eexperimental work was performed at laboratory to investigate the mechanical properties of concrete (compressive strength, splitting tensile strength and flexural strength), first when sprinkle the first layer with water before casting and second when coated with a grout material.The results were investigated and it indicates that, in case of delaying in the time period for casting the second layer, there is a great effect on the mechanical properties of concrete and the use of grout coating material in forced separation has a positive impact on improving its mechanical properties.