STRUCTURES Flashcards
WHAT ARE, AND WHAT KIND OF 4 STATIC LOADS ARE THERE?
APPLIED SLOWLY TO A STRUCTURE AND REACHES A PEEK WITHOUT FLUCTUATING GREATLY.
- DEAD LOADS
- LIFE LOADS
- FOUNDATION LOADS
- IMPACT OR KINETIC LOADS
4 FAILING CONDITIONS OF SEISMIC LOADS?
- SOFT AND WEAK STORIES
- DISCONTINUOUS SHEAR WALLS
- VARIATIONS IN PERIMETER STRENGTH
- REENTRANT CORNER
3 STRESS TYPES TO EXTERNAL FORCE?
- TENSION
- COMPRESSION
- SHEAR
HOOK’S LAW, structures STRESS FORMULA
F = P / A
STRESS = TOTAL FORCE APPLIED / TOTAL AREA
FORCES WITHIN A BUILDING IN A SEISMIC EVENT - FORMULA
FORCES WITHIN A BUILDING IN A SEISMIC EVENT OR EQUAL TO THE WEIGHT OF THE BUILDING.
F = M*A
FORCE (F) = THE MASS (M) OF THE BUILDING x THE HORIZONTAL ACCELERATION (A)
3 structure types FOR SEISMIC RESTRAINT
- MOMENT RESISTING FRAME
- BRACED FRAME
- SHEAR WALLS
10 SEISMIC MITIGATION strategies
- -CONTINUOUS LOAD PATH
- -LOW HEIGHT TO BASE RATIO
- -EQUAL FLOOR HEIGHT
- -SYMMETRICAL PLAN
- -MINIMIZES TORSION
- -UNIFORM SECTION
- -SEISMIC RESISTING ELEMENTS AT PERIMETER
- -SHORT SPANS
- -NO CANTILEVERS
- -NO OPENINGS IN DIAPHRAGMS
3 FUNDAMENTAL PRINCIPLES OF EQUILIBRIUM APPLIED BUILDINGS.
- The sum of all vertical forces acting on a body must equal zero
- The sum of all horizontal forces acting on the body must equal zero
- The sum of all moments acting on the body must equal zero.
Allowable max BEAM STRESS - FORMULA
F = M / S
ALLOWABLE BENDING STRESS = MAX.MOMENT / SECTION MODULUS
MOMENT FORMULA FOR CENTER POINT LOAD
M = P*L / 4
MOMENT = POINTLOAD*LENGTH / 4
MOMENT FORMULA FOR UNIFORM LOAD
M = W*L^2 / 8
MOMENT = UNIFORM LOAD * LENGTH SQUARED / 8
WHAT AFFECTS THE BENDING MOMENT? what not?
LOAD, TYPE OF SUPPORTS & LENGTH AFFECT MOMENT,
Not: MATERIAL AND CROSS-SECTION
SHEAR FORCE FORMULA FOR POINT LOAD
V = W / 2
COLUMN SLENDERNESS RATIO
SLENDERNESS RATIO = L / R
L=Length
R = RADIUS OF GYRATION
SPAN STEEL GIRDERS IN FT
10-70
SPAN Flat wood trusses IN FT
40-150
SPAN Pitched wood trusses IN FT
40-100
SPAN Deep Long span joists IN FT
90-144
SPAN Glued lam beams IN FT
10-60
SPAN FLAT STEEL TRUSSES IN FT
40-300
SPAN PRESTRESSED SINGLE T IN FT
20-120
SPAN Prestress. conc girders IN FT
40-120
SPAN Conc arches IN FT
40-320
SPAN Suspended cables IN FT
450
SPAN Geodesic dome IN FT
400
Coefficient of expansion
expansion of material Measured in inches per degree F
Material specific
Windload formula
Wind load / sf * area normal to wind = windload
Max drift for building during winds/ storms
Should not exceed 1/5000 of the building height
What is a diaphragm
Rigid floor a roof structure transferring lateral loads to vertical shear walls, braced frames, are rigid frames
When vertical - shear wall
Minimum area occupied by columns and/or bearing walls
A Long Span System
- Heavy wood trusses
- Glue lam wood beams, wood arches
- Steel frame, trusses
- Open Web Structural Joists
- Waffle Slab
- Single or Double Tee Concrete
Changes in use over time
Short Span, one Way Systems that can easily be modified
- Light Gauge/Conventional Steel Frame
- Wood systems (including masonry)
- Site Cast 1 way concrete slab • Precast concrete slab
Exposure to Adverse Weather
No reliance on onsite chemical processes
- Steel
- Wood
- Precast Concrete without toppings or grouting
Minimal off-site fabrication time
On-site construction with easily formed materials
- Site cast concrete
- Light Gauge Steel Framing
- Platform Framing
- Masonry
Minimal on-site erection time
A lot of prefab/modular components
- Single story rigid steel frame
- Steel frame with hinged connections
- Precast concrete • Heavy timber frame
1-2 stories with minimal construction time
Lightweight/easy to form/prefab
- Any steel
- Heavy timber frame
- Platform frame
4-20 stories with minimal construction time
Lightwight/easy to form/prefab
- Precast concrete
- Conventional Steel Frame
30+ stories with minimal construction time
Strong, lightweight, easy to assemble
- Steel Frame
- Site/Precast Concrete
Minimal diagonal bracing or shear walls
Rigid Joint System Site cast concrete (With beams/ deep slab around columns
- Single frame w/welded connections
- Single story rigid steel frame
Minimal dead load on foundation
Lightweight/Short Span
- Any Steel
- Any Wood
Minimal structural distress due to unstable foundation
Frame without rigid joints
- Steel frame with bolted connections
- Heavy timber frame
- Precast concrete system
- Platform framing
Concealed Spaces for MEP
Not add height to building
- Truss
- Open web joists
- Light Gauge Steel Framing
- Platform Framing
shear (V) formulas
at apex and any given location
Pointload center formulas
moment an shear
Point Load off center,
moment and shear formulas
point load vs distributed load
shear and moment diagrams
Duration
Shaking duration above a certain threshold acceleration (0.05g)
Velocity of earthquake
Measured in P waves and S waves, P waves are faster
Displacement
Distance that points on the ground are moved from the initial position
Frequenzy
High Frequency Waves
Small velocities and acceleration
Frequenzy
Low Frequency Waves
Large velocities and displacements
typ. periods (seismic)
one second per 10 stories
Ground Amplification:
“Shaking levels at a site may be increased, or amplified, by focusing of seismic energy caused by the geometry of the sediment velocity structure, such as basin subsurface topography, or by surface topography.”
Resonance:
Resonance
“the tendency of a system to oscillate with greater amplitude at some frequencies than at others”
Allowable Beam Deflection
The maximum vertical displacement of the member as it bows under loading. These limits vary depending on code requirements, but may be similar to L/180, L/240, L/360, or L/480
A beam spans 20’. How many inches will it be allowed to deflect if required to meet a maximum of L/240?
20’ * 12” = 240” > 240” / 240 = 1” Allowable deflection
• Gage line
• Gage line: standard dimension from corner edge of an angle to centerline of bolt holes. depends on size of angle
Modulus of Elasticity of steel
29,000,000 psi
Modulus of Elasticity of wood
± 1.100.000 psi
area of circle
A = π r²
area of sphere
A=4πr2
1 kip/in2. = ? psi
1 kip-force/square inch = 1000 psi
High-Strength steel bolts
A325 & A490
Unfinished steel bolts
A307
he A307 bolts were once the standard for all applications, but are currently used predominantly for secondary uses that do not require the high strength provided by A325 or A490 bolts.
Pressure P formula
Pressure P is defined as
P=F/A
where F is a force applied to an area A that is perpendicular to the force.
