Presentation on theme: "TOPIC 1.3 RESPONSE OF CIVIL ENGINEERING PROJECT. FORCE IN CIVIL ENGINEERING PROJECT A) Identify the system response: ● Sway ● Deflection and ● Vibration."— Presentation transcript:
FORCE IN CIVIL ENGINEERING PROJECT A) Identify the system response: ● Sway ● Deflection and ● Vibration B)Identify the component response: ● Buckling ● Torsion ● Shortening ● Elongation, ● Shearing and ● Bending Learning Outcomes
System Response i. Sway ii. Deflection iii. Vibration
(i) Sway Definition : move back and forth, swing,lean in a certain direction; be inclined toward. to move or swing to and from, as something fixed at one end or resting on a support.
Impact of wind load Tacoma Narrows Bridge collapse
Definition : is a term that is used to describe the degree to which a structural element is displaced under a load. Deviation, diversion, turning aside (ii) Deflection
Deflection of Beams Excessive deflections are unacceptable in building construction; can cause cracking of plaster in ceilings and can result in jamming of doors and windows. Most building codes limit the amount of allowable deflection as a proportion of the member's length, i.e. 1/180, 1/240 or 1/360 of the length. (ii) Deflection
Definition : mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road. More often, vibration is undesirable, wasting energy and creating unwanted sound – noise. (ii) Vibration
Such vibrations can be caused by imbalances in the rotating parts, uneven friction, the meshing of gear teeth, etc. Careful designs usually minimize unwanted vibrations. (ii) Vibration
Types of vibration Free vibration -occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. -e.g ; pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. (ii) Vibration
Types of vibration Forced vibration -occur when an alternating force or motion is applied to a mechanical system. -e.g ; vibration of a building during an earthquake. -In forced vibration the frequency of the vibration is the frequency of the force or motion applied, with order of magnitude being dependent on the actual mechanical system. (ii) Vibration
(1) BUCKLING Definition : In engineering, buckling is a failure mode characterized by a sudden failure of a structural member subjected to high compressive stresses, where the actual compressive stresses at failure are smaller than the ultimate compressive stresses that the material is capable of withstanding. This mode of failure is also described as failure due to elastic instability.
(2) TORSION Definition : twisting, winding, bending, distortion, contortion In solid mechanics, torsion is the twisting of an object due to an applied torque. In circular sections, the resultant shearing stress is perpendicular to the radius.
(3) SHORTENING Definition : make shorter, abbreviate, cut, truncate; become shorter Cause of shortening (i) elastic stresses (ii) shrinkage (iii) creep
The shortening of the column if its initial height is 5m. and Force 2000kN Example of shortening
(4) ELONGATION Definition : lengthening, extension, making longer an addition to the length of something When a material is tested for tensile strength it elongates a certain amount before fracture takes place. The function of this test is to measure the ductility of steel.
(5) SHEARING Definition : is defined as a stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly Shear stress is the outcome of sliding one part over the other in opposite directions. The rivets and bolts of an aircraft experience both shear and tension stresses
The formula to calculate average shear stress is: where τ = the shear stress; F = the force applied; A = the cross sectional area.
Example of shearing Failure of short column by oblique shear
(6) BENDING Definition : crouching, stooping; curving, twisting; contortion, distortion. In engineering mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to an axis of the element.