Studied by 222 peopleWhy is carbon content important to steel quality?
carbon content is a crucial determinant of the properties of a ferrous (iron-based) metal too much carbon makes a hard but brittle metal too little carbon produces a soft, relatively weak material
How are steel structural shapes formed?
in the structural mill hot steel blank passes through a succession of rollers the rollers squeeze the metal into progressively more refined approximations of the desired shape and size
What are the most common steel beam shapes?
wide-flange shapes are used for most beams and columns, superseding the older American Standard (I-beam) shapes
How do you find the depth and width of a wide flange shape?
depth is the nominal first number after the W width must be looked up in the Manual of Steel Construction
How are open-web steel joists formed?
prefabricated steel trusses designed to carry heavy loads, particularly bays of steel joists
What are the four series of open-web steel joists?
K series joists Longer-span LH and DLH series joists CJ composite joists
What are the ways of joining steel members?
Rivets Bolts Welds
Rivet
a steel fastener consisting of a cylindrical body and a formed head
How are rivets used to join steel members?
it is brought to a white heat in a forge inserted through holes in the member to be joined hot worked with a pneumatic hammer to produce a second head opposite the first as the rivet cools, it shrinks, clamping the joined pieces together and forming a tight joint riveting was for many decades the predominant fastening technique, but it has been replaced by the less labor intensive techniques of bolting and welding
What are the two categories of bolts commonly used in steel frame connection?
carbon steel bolts high-strength bolts
Carbon steel bolts
similar to the ordinary machine bolts that can be purchased in hardware stores
High-strength bolts
heat treated during manufacture to develop the necessary strength inserted into holes slightly larger than the shank diameter of the bolt and then various ways can be used to determine if they bolt is tightened to the necessary tension to transfer the load
How is welding used to join steel members?
welding can join the members of a steel frame as if they were a monolithic whole welded connections, properly designed and executed, are stronger than the members they join in resisting both shear and moment forces
How do you know high strength bolts are tightened correctly?
pneumatic impact wrench turn-of-nut method load indicator washer tension control bolt swaged lock pin and collar fastener
What are the edges of steel members beveled for?
a beveled edge allows full access for the welding electrode so that the joint can be filled with weld metal to the same thickness and strength as the member being connected
Moment connection
a joint that allows the transfer of bending moment forces between a column and a beam connection of flanges strongly across the joint by means of a full-penetration groove welds across the beam flanges
framed connection
a beam is connected to a girder or a stanchion by means of two angles placed on the two sides of the web of a beam joins only the web of the beam and not the flanges
How do you stabilize a steel frame against lateral loads?
diagonal bracing eccentric bracing moment connections shear panels
How do you attach a steel column to a foundation?
steel baseplates, which distribute the concentrated loads of the steel columns across a larger area of the concrete foundation, are shop welded to all but the largest of columns the baseplate is then attached to the foundation with anchor bolts cast into the foundation
How do you plumb-up a steel frame building?
plumbing up is straightening and squaring the steel frame in order to make sure that the frame is level overall the two-story pier of framing is them plumbed-up with diagonal cables and turnbuckles while checking the alignment with plumb bobs, transits, or laser levels
Why are columns spliced at waist level?
column splices are made at waist level above this platform, both as a matter of convenience and as a way of avoiding conflict between the column splices and beam-to-column connections
What materials can be used to fireproof steel members?
brick concrete metal lath and plaster gypsum board spray-on fireproofing loose insulating fill inside a sheet metal enclosure water-filled box column made of a wide-flange shape with added steel plates rigid slab fireproofing suspended plaster ceiling mineral fiber slabs intumescent mastics and paints
What are some types of improved beams?
castellated beams plate girders rigid frames
Castellated beams
produced by flame cutting the web of a wide-flange section along a zigzag path, then reassembling the beam by welding its two halves point to point, thus increasing its depth without increasing its weight
Plate girders
long-span beams tailored to any loading condition custom designed and fabricated
Rigid frames
efficiently produced by welding together steel wide-flange sections or plate girders
How do tensile structures work?
a tensile structure is a membrane that is supported by masts or other rigid structural elements such as frames or arches the fabric and cables transmit external loads to the rigid supports and ground anchors by means of tensile forces
How are light gauge steel framing members produced?
cold-formed to differentiate from the much heavier hot-rolled shapes that are used in structural steel framing
What shapes does light gauge steel framing come in?
C-shaped sections: studs, joists, rafters Runner channel sections: top and bottom track
Why is gauge of the steel important?
the strength and stiffness of a member depends on the shape and depth of the section and the gauge (thickness of the steel sheet from which it is made
How is welded wire fabric used?
a reinforcing mesh of welded wire fabric, cut to a size just a bit smaller than the dimensions of the slab, is laid over the moisture barrier or crushed stone the fabric most commonly used for lightly loaded slabs the grid of wires and bars helps protect the slab against cracking that might be caused by concrete shrinkage, temperature stresses, concentrated loads, frost heaving, or settlement of the ground beneath
Why are control joints important for a slab on grade?
control joints must be provided at intervals in a slab on grade the function of a control joint is to provide a place where the forces that cause cracking can be relieved without disfiguring the slab the reinforcing mesh is discontinued at each control joint as a further inducement for cracking to occur in this location rather than at random
control joint
a straight, intentional crack that is formed before the concrete has hardened fully
How do form ties work?
form ties are inserted through holes provided in the formwork panels and secured to the back of the form by devices supplied with the form ties the ties will pass straight through the concrete wall from one side to another and remain embedded permanently in the wall after it is poured
Form ties
small-diameter steel rods specially shaped to hold the formwork together under the pressure of the wet concrete
What are the types of formwork used?
wall forms may be custom built of lumber and plywood for each job, but it is more usual to use standard prefabricated formwork panels insulating concrete forms lift-slab construction flying formwork slip forming tilt-up construction
Insulating concrete forms
an alternative way of casting a concrete wall, particularly one that will be an exterior wall of a building, is to use insulating concrete forms that serve both to form the concrete and to remain in place permanently as thermal insulation
Lift-slab construction
used chiefly with two-way flat plate structures, virtually eliminates formwork the floor and roof slabs of a building are cast in a stack on the ground the hydraulic jacks are used to lift the slabs up the columns to their final elevations, where they are welded in place using special cast-in-place steel slab collars
Flying formwork
for slabs that are cast in place, flying formwork is fabricated in large sections that are supported on deep metal trusses the sections are moved from one floor to the next crane, eliminating much of the labor usually expended on stripping and re-erecting formwork
Slip forming
useful for tall walled structures such as elevator shafts, stairwells, and storage silos a ring of formwork is pulled steadily upward by jacks supported on the vertical reinforcing bars, while workers add concrete and horizontal reinforcing in a continuous process
Tilt-up construction
a floor slab is cast on the ground, and reinforced concrete panels are poured over it in a horizontal position when curing is complete, they are hoisted into position by a crane and grouted together, thereby eliminating most of the usual wall formwork
How are concrete columns formed?
the column form may be a square box of plywood or composite panels, a cylindrical steel or plastic tube bolted together in halves so that it can later be removed, or a waxed cardboard tube that is stripped after curing by unwinding the layers of paper that make up the tube
Why are reinforcing bars offset at the top of columns?
where vertical bars overlap, the tops of the bars from the column below are offset (bent inward) by one bar diameter to avoid interference
What are the various types of one-way floor and roof framing systems?
one-way solid slab system one-way concrete joist system (ribbed slab) wide-module concrete joist system
One-way solid slab system
spans across parallel lines of support furnished by walls and/or beams
One-way concrete joist system (ribbed slab)
as one-way solid slab spans increase, a progressively thicker slab is required beyond a certain span, the slab becomes so thick that the weight of the slab itself is an excessive burden, unless a substantial portion of the nonworking concrete in the lower part of the slab can be eliminated to lighten the load the bottom steel is concentrated in spaced ribs or joists the thin slab that spans across the top of the joists is reinforced only by shrinkage-temperature bars there is little concrete in this system that is not working, with the result that are one-way concrete joist system can span considerably longer distances than a one-way solid slab
wide-module concrete joist system
when fire resistance requirements of the building code dictate a slab thickness of 4.5" or more, the slab is capable of spanning a much greater distance than the normal space between joists in a one-way concrete joist system joists are spaced 4-6' apart
What is special about two-way floor and roof framing systems?
two-way concrete framing systems are generally more economical than one-way systems in buildings where the columns can be spaced in bays that are square or nearly square in proportion
What are the various types of two-way floor and roof framing systems?
two-way flat slab two-way flat plate system two-way waffle slab system
Two-way flat slab
a system suited to heavily loaded buildings such as storage and industrial buildings this formwork is completely flat except for a thickening of the concrete to resist the high shear forces around the top of each column traditionally, this thickening was accomplished with both a funnel shaped mushroom capital and a square drop panel, but today the capital is usually eliminated to achieve a greater economy of formwork cost leaving a drop panel to do the work alone
Two-way flat plate system
in more lightly loaded buildings the slab need not be thickened at all over the columns because there are no beams and girders, only a thin slab, the story heights of the building may be kept to an absolute minimum
Two-way waffle slab system
the waffle slab, or two-way concrete joist system, is the two-way equivalent of the one-way concrete joist system metal or plastic pans called domes are used as formwork to eliminate nonworking concrete from the slab, allowing considerably longer spans than are feasible n the two-way flat plate system
What are the innovations in sitecast concrete?
lightweight concrete and admixtures formwork materials and methods lift-slab flying formwork gang forms slip forms tilt-up shotcrete
What are the spanning differences of the different precast floor elements?
solid slabs - short spans and minimum slab depths hollow-core slabs - intermediate spans single tees - longest spans double tees - longest spans
What are topping slabs used for?
after the slab elements have been erected, a concrete topping is poured over them and finished to a smooth surface the topping, usually 2" in thickness, bonds during curing to the rough top of the precast elements and becomes a working part of their structural action the slab elements may be topped or untopped
What are the standard precast concrete beam and girder shapes?
rectangular beam L-shaped beam inverted tee beam AASHTO beam
How are stirrups at the top of precast elements used?
mild steel reinforcing bars are used for stirrups the projecting tops of the stirrups will bond to the sitecast topping
Why are L-shaped and inverted T-shapes important?
the projecting ledgers on L-shaped beams and inverted tees provide direct support for precast slab elements they conserve headroom in a building by supporting slabs near the bottoms of the beams, as compared to rectangular beams without ledgers, where slab elements must rest on top
What is used to connect precast elements?
bolting welding grouting the simplest joints in precast concrete construction are those that rely on gravity by placing one element atop another, as is done where slab elements rest on a bearing wall or beam, or where a beam rests on the corbel of a column posttensioning can be used to combine large precast elements into even larger ones on the site
What is posttensioning used for in precast beams?
a posttensioned, structurally continuous beam-column connection may be created by passing a tendon from a pocket in the top of one beam, through the column, to a pocket in the top of the other beam the tendon is anchored to a plate in one pocket as it is tensioned by a jack in the other pocket
Why is a masonry cavity wall important?
a cavity wall prevents water from reaching the interior of the building by interposing a cavity between the outside and inside wythes of the wall insulation reduces dead weight
What is an advantage of using adjustable masonry ties?
adjustable masonry ties are convenient for the masons because they allow for irregularities in course heights
What is a disadvantage of using adjustable masonry ties?
they may be insufficiently rigid for some structural purposes
Where are internal flashings used?
typically at the bottom of a cavity wall at every location where the cavity is interrupted, such as: above the heads of windows and doors below copings and window sills below lintels and above shelf angles over spandrel beams
What happens when an internal flashing meets the exterior surface of a masonry wall?
the flashing should be carried at least 3/4" beyond the outside face of the wall flashing should be turned down at a 45 degree angle so that draining water drips free of the wall if the internal flashing is made of a flexible material, it should be cemented to a sheet metal flashing just before it exits the wall
What are end dams used for?
to keep water from running off the ends of sill and lintel flashings
Why are high quality flashing materials important in masonry walls?
flashings within a wall are almost impossible to replace if they should fail in service even the most expensive flashing materials cost only a very small fraction of the total price of a masonry wall, so there is little reason to use cheap ones in a misguided effort to save money
What spanning systems may be supported on masonry bearing walls?
wood balloon framing heavy timber framing structural steel framing sitecast concrete framing precast concrete framing
Which masonry units shrink after installation and which expand?
new clay masonry units tend to absorb water and expand under moisture conditions new concrete masonry units usually shrink somewhat as they give off excess water following manufacture
Does brick masonry have any tensile strength?
no, the allowable tensile strength of brick is 0 psi
Does reinforcing need to remain continuous through an expansion joint and control joint?
joint reinforcing must be interrupted at movement joints so that it does not restrain the opening or closing of the joint
What does efflorescence indicate?
water has begun to enter the wall best controlled by investigating and correcting the source of leakage
What do you need to do to mortar when outdoor temperatures are below freezing?
warming the mixing water (and sometimes the sand as well) to produce mortar at the optimum temperature for working and curing enclosure using a Type III (high early strength) cement to accelerate the curing of mortar mixing the mortar in smaller quantities so it does not cool excessively before it is used chemical accelerators and so-called "anti-freeze" admixtures are, in general, harmful to mortar and reinforcing steel and should not be used
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