Structures 2 Quiz Questions

What is the structural function of rebar lugs?

to improve the bonding between concrete and steel

What is the structural function of the longitudinal rebars in RC beams?

to resist tension stress

What type of cement is appropriate for construction of a wastewater treatment plant?

Type V

In concrete construction, what does the cylinder test measure?

concrete compressive strength

Which of the following design codes and standards is used in the U.S. for designing reinforced concrete structures?

ACI 318

in a building structure, how can you tell whether a column is a slender column or a short column?

when the column’s compressive strength is higher than its buckling strength, it’s a slender column.

What is the primary structural function of a hold-down in a wood shear wall?

to resist uplift from the over-turning moment

In accordance with the current IBC building code, what is the minimum distance between the grade and top of slab?

8”

For a 2×6 stud wall, which of the following section property numbers would you use to calculate the stud’s buckling capacity?

20.80

While the platform framing is typically preferred in wood building construction, in which of the following areas is balloon framing necessary?

exterior walls adjacent to atrium

structural steel currently cost $5000 per ton (1 ton=2000 lbs). We need to order a 40-foot long W18X60 steel beam. How much do we expect to pay for it?

$6,000

What is the purpose of a ‘long lead” package in steel construction?

To order steel ahead of final design completion

What is the most common type of steel used in building structures?

carbon steel

If you see A7 steel listed in the record drawings of an existing multi-story office building in downtown Los Angeles, what kind of structure is it?

A historic building structure

A multi-story commercial building structure in downtown Los Angeles, why is the ground floor floor-to-floor height typically much larger than the upper floors?

Because the ground floor can be used for commercial purpose to generate more rent.

which of the following does NOT affect the load capacity of a column?

the design live load

Which of the following measures can reduce a wood beam’s mid span deflection?

increase the width of the beam section

In order to hang a lighting fixture from a wood ceiling beam, your contractor suggested two options. Option 1 is to hang the fixture with a steel wire attached to an eyebolt screwed into the bottom of the beam. Option 2 is to use a thru eyebolt with the nut bearing on top of the beam. Which option should you approve?

option 2

what is the most common spacing of wood roof joists?

24”

where does the maximum compressive bending occur on this beam?

D

wood construction PROS

1. 1. Largest building inventory

2. 2. only renewable resource

3. 3. lightest structural material (25~50 #/ft³)

4. 4. tolerant of human errors (cut, trim replace)

wood construction CONS

fire risk, combustible (ok for small jobs)

wood types

1. 1. natural “sawn” lumber

2. 2. engineered wood (truss joist, PSL/LVL, plywood/OSB)

soft wood

needle leaf, evergreen, abundant, cheaper, structures

Hard wood

broad leaf, deciduous, architectural

nominal size - wood

used price

(2×8) → 1 1/2” x 7 1/2”

actual size - wood

used for design

2×8 → (1 1/2” x 7 1/2”)

WWPA

Western Wood Product Association

creates grade rules

IBC

International Building Code

governs design behavior

wood design capacities

tension, compression, bending, shear

T/F: wood can sustain parallel stress in tension

true

T/F: wood can sustain perpendicular stress in compression, but is weaker than parallel stress in compression

true

T/F: only shear tension can cause cracking in wood

true

tensile stress

ft = W (#) / A(M²)

strain

=Δ/L

“Box” system

bearing wall/shear wall system

Horizontal Diaphragm and Vertical Diaphragm

most common system

Platform Framing

• double top plate

• west USA

• stressed skin structure

balloon framing

• continuous stud

• temporary bracing/shoring

• east USA

member size rule of thumb (wood beam)

d = L/20 ±

lamellas

short wood pieces for long spans

member size rule of thumb (wood column)

thickness = height/10 ±

member size rule of thumb (wood wall)

thickness = L/15 ~L/30 ±

dry construction

steel and wood

steel is made of

Iron (Fe) + Carbon (C)

steel manufacturing

• Iron ore → blast furnace → steel

• produces (bar) billet, boom, slab

slag (recycled for concrete)

impurity from steel manufacturing process

recycled for concrete

steel slab

cold form, light gauge metal steel (LGS) stud

steel bar/boom

reheat and fed into teeming ladle and hot rolled into shape

shop drawing

by fabricator, for cut and drill holes

carbon steel

• most common

• mild steel

• normal strength

High Strength Low Alloy Steel

• carbon + allow

• improves bonding

• higher strength

Alloy Steel

• carbon + alloy + heat

• used for bolts/connectors

steel corrosion solutions

• stainless (carbon steel + chromium)

• paint primer

• galvanizing (steel + zinc coat) - only needed when exposed to the elements

steel fire protection

• concrete confinement

• spray-on fireproofing - fiber particle

• drywall confinement

• intumescent paint ($$$)

T/F: Steel is non-combustible and not fire resistant

true

Building structural systems (steel)

bearing wall/shear wall

braced frame systems (BF)

moment frame (MF)

dual system

Brace Frame systems

provides strength/stiffness

shapes: chevron, x - bracing, diagonal, v - brace

Moment Frame

rigid joint

more ductile

more $$$, bigger members

Dual System

required for high rise

bearing/shear wall + moment frame OR braced frame system + moment frame

Eccentric Braced Frame

combines the elastic stiffness of a CBF with the ductility of a MF.

Creates a link beam by offsetting braces, link will dissipate energy

concrete aggregate grading

uniformly graded, well graded, gap graded

concrete grading goal

minimum voids

minimum cracks

minimum need for cement

hydraulic cement (portland cement)

cement + H20 → bonding agent (paste)

invented by Joseph Aspdin in 1824

Portland cement manufacturing

limestone (crushed and blended) → heated in kiln → fused limestone (ground into power) → cement

*Damaging to environment

I (Types of Cement)

Regular - used for general construction and considered standard utility cement

II (Types of Cement)

Moderate Heat & Sulfate Resistant - used for foundations when cement comes into contact with soil or groundwater, generates less heat during curing

III (Types of Cement)

High Early Strength - hardens and gains strength much faster than Type I. Formwork can be removed quickly.

IV (Types of Cement)

Low Heat - used in mass concrete structures like damn. Produces less heat while curing, prevents cracks

V (Types of Cement)

High Sulfate Resistant - used for things close to ocean water or wastewater. Resists sulfate attacks from soil or water.

concrete curing process

initial harden in 2-4 hrs

7-14 days to strip formwork

design strength (fc’) reached in 28 days, but will continue to strengthen over time

water cement ratio (w/c)

lower w/c ratio the higher the strength

higher w/c ratio the better the workability

admixtures

chemicals to improve conc. quality (high early strength, air entraining agent, water reducing admixture)

T/F: concrete is bad in compression but good in tension

false

T/F: rebar sizes are 1/8” of their number

true (#3 → 3/8”)

cylinder test

measures the compressive design strength (fc’) of concrete

slump test

ideal slump = 3”-6”

most common = 3” (foundation) - 4” (column/beam)

high slump = better

ASD

Allowable Stress Design

USD

Ultimate Strength Design

more logical, dead and live load treated differently, produce smaller members

LRFD

Load Resistance Factored Design - steel

ACI 318 Code

American Concrete Institute’s standard