A rectangular concrete beam has dimensions b=16 in. and h=30 in. The location of the Gr. 60 reinforcing bars, which are placed all in one row in the bottom of the section, is d=27 in. Using a specified compressive strength of concrete of 5,000 psi and the assumptions and simplifications of the ACI 318-14 Code, find the nominal flexural strength Mn for positive bending if the reinforcing bars are: a. Three No. 9 bars b. Four No. 9 bars c. Three No. 8 + two No. 10 bars d. None (i. e., the beam is unreinforced)

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.