Civil Engineering

88 flashcards by MentisLibrary

Structures, concrete, soil mechanics, surveying, hydraulics, and transportation in one deck. The breadth a civil engineer is expected to carry, with typical field values on the cards that need them.

What are the four primary load categories a structural engineer must consider?
Dead loads (permanent self weight), live loads (occupancy and movable), environmental loads such as wind and snow, and seismic loads from ground motion.
What is a load path?
The continuous chain of structural elements that carries a load from where it is applied down to the foundation and into the soil.
How do you tell if a plane truss is statically determinate?
Compare members plus reactions to joint equations: if m + r equals 2j the truss is determinate, if m + r is greater than 2j it is indeterminate, and if less it is unstable.
What is the general condition for static determinacy of a plane frame?
A plane frame is determinate when the number of unknown reactions and internal forces equals the number of available equilibrium equations, three per free body plus condition equations from internal hinges.
Why are indeterminate structures often preferred over determinate ones?
They provide redundancy, so the loss of one member or the formation of one plastic hinge does not necessarily cause collapse, and they usually deflect less.
What does the flexure formula give for a beam in bending?
The bending stress at a distance y from the neutral axis, equal to the moment times y divided by the moment of inertia.
What is the relationship between load, shear, and moment along a beam?
The slope of the shear diagram equals the load intensity, and the slope of the moment diagram equals the shear.
What is the maximum moment for a simply supported beam with a uniform load?
Moment at midspan equals w L squared divided by 8, with end reactions of w L over 2.
What is Euler buckling of a column?
Elastic instability of a slender axially loaded column, where the critical load depends on stiffness and effective length, not on material strength.
What is the slenderness ratio of a column?
The effective length divided by the radius of gyration of the cross section, the key parameter separating short crushing failures from long buckling failures.
What assumption defines an ideal truss analysis?
All members are pin connected and loads are applied only at joints, so every member carries only axial force.
How do you identify zero force members in a truss?
At an unloaded two member joint both members are zero force, and at an unloaded three member joint with two collinear members the third member is zero force.
What is tributary area and how is it used?
The floor area whose load is carried by a given beam, girder, or column, found by halving the distance to adjacent supporting members.
What is the difference between wind load and seismic load in origin?
Wind is an externally applied pressure on the building surface, while seismic force is an inertial force generated by the building's own mass responding to ground acceleration.
Why is ductility so important in seismic design?
Because it lets a structure absorb and dissipate earthquake energy through inelastic deformation without collapsing, permitting design for forces much lower than fully elastic demand.
What is a diaphragm in a building structure?
A floor or roof system acting as a horizontal beam that collects lateral load and distributes it to vertical elements such as shear walls or frames.
What is the water-cement ratio and why does it dominate concrete quality?
The mass ratio of mixing water to cementitious material, which controls capillary porosity and therefore strength, permeability, and durability.
What does the concrete slump test measure?
Workability or consistency of fresh concrete, measured as the vertical slump of a cone of concrete after the mold is lifted.
At what age is concrete compressive strength normally specified?
At 28 days, using standard cured cylinders tested in compression.
Why must concrete be cured, and what does curing actually do?
Curing maintains moisture and favorable temperature so cement hydration can continue, developing strength and reducing permeability and cracking.
What are the roles of the main ingredients in a concrete mix?
Cement and water form the paste that binds, fine aggregate fills voids between coarse aggregate, coarse aggregate provides bulk volume and dimensional stability, and admixtures modify behavior.
Why is reinforcing steel placed in the tension zone of a concrete member?
Because concrete is strong in compression but weak and brittle in tension, roughly one tenth of its compressive strength, so steel carries the tensile force after concrete cracks.
What is concrete cover and why does it matter?
The clear distance from the concrete surface to the nearest reinforcing steel, which protects rebar from corrosion and fire and develops bond.
What is a balanced reinforcement ratio, and why do codes require less than that?
The ratio at which concrete crushing and steel yielding occur simultaneously. Codes require sections to be tension controlled with less steel so the steel yields first.
What is development length in reinforced concrete?
The embedment length of a bar needed to transfer its force to the concrete by bond so the bar can reach yield without slipping.
What is prestressed concrete and what problem does it solve?
Concrete precompressed by high strength tendons so that service loads reduce the compression rather than producing net tension, largely eliminating cracking.
What is the difference between pretensioning and post-tensioning?
Pretensioning stresses the strands before the concrete is cast and relies on bond after release, typically in a precast plant. Post-tensioning stresses tendons in ducts after the concrete has cured, usually on site.
What causes prestress losses over time?
Elastic shortening at transfer, plus long term concrete creep and shrinkage and steel relaxation, along with friction and anchorage seating in post-tensioning.
Why is structural steel usually more efficient than concrete for long spans?
Steel has a much higher strength to weight ratio, so less self weight is carried over the span and members are shallower and lighter.
What are the two main limit states for a steel beam in bending?
Yielding of the cross section, reaching the plastic moment, and lateral torsional buckling of the compression flange.