Cho cấu kiện bê tông cốt thép chịu nén có f’c(Mpa), khối lượng riêng wc(T/m3 ). Cấu kiện được thi
công trong môi trường không khí có độ ẩm H(%). Bảo dưỡng bằng hơi nước, khi cường độ bê tông đạt 70% theo thiết
kế, kết cấu chịu tải trọng thường xuyên gây ra ứng suất nén là 18Mpa.
a) Sau bao nhiêu ngày kết cấu bắt đầu chịu tải? (tính tròn ngày).
b) Biến dạng từ biến sau 600 ngày là bao nhiêu? Biết: Hệ số ks=1.025

Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.

Which of the following controllers anticipates the future from the slope of errors over time? a)-proportional b)-on/off c)-integral d)-derivative.

Athin walled concentric tube exchanger is used to cool engine oil from 160°c to 60°c with water that is available at 25°c acting as a coolant. the oil and water flow rates are each at 2 kg/s, and the diameter of the inner tube is 0.5 m and the corresponding value of the overall heat transfer coefficient is 250 w/m2. oc. how long must the heat exchanger be to accomplish the desired cooling? cpwater=4.187 kj/kg-candcpengine el=2.035 kj/kg·°c, oil . 120]