G-4 Slabs Flashcards
Slab-on-grade
edge form that defines the shape of slab ontop of a well compacted sub grade that supports the slab. along with suitable reinforcement
Monolithic slab-on-grade
- used in residential and commercial
- can be very economical and quick to form in place
- ## footing portion and floor portion under different loads
Isolated slb-on-grade
- poured after footings and walls have been placed
- typically an isolation joint will be places between slab and footing along with air and moisture barrier
Ground prep
- slab is only as strong as material its placed upon
- if ground is suitable it only needs to be excavated down and levelled to grade
- different type of sub grade must be laid down if original is not smooth enough
- if soil is not suitable it must be dug out and replaced with better fill and compacted properly
Forming
can be as easy as using 2x4 or 2x12 planks and metal or wood stakes to brace and straighten
- poured after footings and walls have been places
- typically an isolation joint will be places between slab and footing along with air and moisture barrier
Isolated slab - on - grade
- used in residential and commercial
- can be very economical and quick to form in place
- footing portion and floor portion under different loads
Monolithic slab-on-grade
slab thickness strength and design are stated in drawings by?
Engineer
strength of slab are related to?
- base prep
- compressive strength of concrete mix and proper curing
Durability
many industrial buildings require treatments to increase durability against continuos traffic and heavy loads
interior slab durability
admixtures may be added to the mix to protect from chemicals, oils, greases. powdered or mechanical hardeners can be applied to the surface of slab during finishing
Exterior slab durability
air entrainment is specified for all exterior concrete exposed to freeze thaw cycles. adds microscopic air bubbles to concrete which can expand and contract without great risk of damage.
Reinforcement for slab on grade
BCBC does not require reinforcement on slab on grade but many carpenters put in anyway
- concrete in contact with ground rebar should be kept 3” (75mm) off the ground along with poly vapour barrier
Elevation of exterior slab on grade
must be low enough not to cause meltwater or stormwater to back up and enter building
- should be sloped at least 1/8th per foot
elevation on interior slabes
required by BCBC to have bottom of slab higher then top of perimeter drain
Isolation joint
Expansion/contraction isolation joint
give and take strips
should be placed in slabs at least every 15m (50’) used to isolate one concrete member from another and designed to allow for vertical and horizontal movement.
Controle Joints
is weakening in concrete slab that is designed to control natural cracking due to shrinkage.
- driveways and garages: 3m apart
- sidewalks : 1.5 m apart
Flate plate slab (suspended)
- simplest for of suspended slab
- stays same thickness throughout and when stripped has no distinguishing features in the soffit
- free spans from support to support
- relies only on its own strength and rebar to hold it up.
Flat slab (suspended)
- columns that hold up slab will have either a column capital or drop panel or both to help support slab
- these at as shear support and act to reduce span of slab and will allow columns to be further spaced apart
One way slab
- slab where there is some sort of support from column to column. spans fro beam to beam
- load carrying steel in slab runs perpendicular to the beams
two-way slab
load carrying steel runs in both directions
One way Ribbed slab
- uses series of metal pans secured end- to- end to the slab deck to create a joist pattern in slab.
- the ribs or joists are poured monolithic with slab to allow slab to be quite thin
- when stripped you can see joist shaped can be seen running from beam to beam
two way ribbed slab
- sam except dome pans are installed an to create grid pattern.
- when stripped creates a waffle pattern
Girders
Span from column to column
Intermediate beams
span between girders
Spandrel beam
beam at perimeter of slab
Capital forms
designed to attach to the columns formwork at the top
Concrete shoring
shoring is used to insure safety for workers and quality .
shoring system is referred to as falsework and supports the formwork concrete structure.
Falsework
is a structure in its self
- requires its own foundation vertically and horizontally with bracing
difference between falsework and formwork
- not always clear
- by definition falsework supports the form work
falsework is everything put in place so a suspended slab can happen
Sigle vertical shore
- normally 4x4 wood used as vertical support
- cut 1 and a half inches short to allow pair of wedges used to adjust shore length
Slenderness ratio
- each single shore may require horizontal braces along height.
- braces are used to prevent blowout
MUST NOT EXCEED 1:50 meaning 1 is minimum cross sectional dimensions and 50 is the unsupported height of shore
Ex task is to shore up vertical distance of 18’
- turn feet into inches 18x12= 216”
- then divide by slenderness ratio *if answer is more then 4 posts need to be laterally braces
- 216/18= 4.32”
- therefor posts must be laterally supported
ellis Clamps
two wooden shores can be joined and made adjustable by ellis clamps
- ellis clamp is metal clamp used to transfer load from one 4x4 post to another joined post
- as force enters top of shore, the right handed side of clamp is forced down and clamp is tightened up
steel shore
- Single telescopic steel shores are often used in falsework
- can adjust height with rotating riser
Scaffold shoring
- strength of metal and speed at which it can be set up makes its the most economical system for falsework .
- must be approved by engineer
Flying forms
- big scale projects have pre fab formwork
- two types
- gang forms: used for forming walls
- slab tables: used to form suspended slabs
both made from combining wood and metal.
Aluma-beam
- aluminum extrusion that is in the shape of an i-beam
- has wooden 2x2 at top and a groove at bottom that will accept the head of a bolt to fasten it to scaffold shoring
