consists notes for the frequently asked questions for structure 6 in architecture. scheme 2009 types of welded joints. difference between limit state and working stress method laterally supported and unsupported beam tension and compression members. fire protection for steel members. advantages and disadvantages of bolted connections brackett connections

1. STRUCTURES 6 NOTES

2. Types of riveted joints
Riveted joints are mainly of two types
• 1. Lap joints
• 2. Butt joints
Lap Joints:
The plates that are to be joined are brought face to face such that an overlap exists. Rivets are inserted
on the overlapping portion. Single or multiple rows of rivets are used to give strength to the joint.
Depending upon the number of rows the riveted joints may be classified as single riveted lap joint, double
or triple riveted lap joint etc. When multiple joints are used, the arrangement of rivets between two
neighbouring rows may be of two kinds. In chain riveting the adjacent rows have rivets in the same
transverse line. In zig-zag riveting, on the other hand, the adjacent rows of rivets are staggered.

3. Butt Joints
In this type of joint, the plates are brought to each other without forming
any overlap. Riveted joints are formed between each of the plates and one or two
cover plates. Like lap joints, the arrangement of the rivets may be of various kinds,
namely, single row, double or triple chain or zigzag. The strength of a rivet joint is
measured by its efficiency. The efficiency of a joint is defined as the ratio between the
strength of a riveted joint to the strength of an unrivetted joints or a solid plate.
Obviously, the efficiency of the riveted joint not only depends upon the size and the
strength of the individual rivets but also on the overall arrangement and the type of
joints.

4. DIFFERENCE BW LIMIT STATE AND WORKING STRESS (RCC DESIGN COMPONENTS)
LIMIT STATE METHOD
• The stresses are obtained from
designloads and compared with
designstrength.
• In this method, it follows linear
strainrelationship but not linear
stressrelationship (one of the major
differencebetween the two methods
of design).
• The ultimate stresses of materials
itself are used as allowable stresses.
• The material capabilities are not
underestimated as much as they are
in workingstress method. Partial
safety factors are used in limit state
method.
WORKING STRESS METHOD
• The Stresses in an element is
obtainedfrom the working loads and
comparedwith permissible stresses.
• The method follows linear stress-
strainbehaviour of both the materials.
• Modular ratio can be used to
determineallowable stresses.
• Material capabilities are under
estimatedto large extent. Factor of safety
are usedin working stress method.
• The member is considered as
workingstress.
• Ultimate load carrying capacity cannot
bepredicted accurately.
• The main drawback of this method is
thatit results in an uneconomical section.

5. LATERALLY SUPPORTED AND UNSUPPORTED BEAM
Under increasing transverse loads, a beam should attain its full plastic
moment capacity. This type of behavior is seen in a laterally supported
beam.
Two important assumptions have been made therein to achieve the ideal
beam behaviour.
They are:
• The compression flange of the beam is restrained from moving laterally;
and
• Any form of local buckling is prevented.
However, a beam experiencing bending about major axis and its
compression flange not restrained against buckling may not attain its
material capacity. If the laterally unrestrained length of the compression
flange of the beam is relatively long then a phenomenon known as lateral
buckling or lateral torsional buckling of the beam may take place and the
beam would fail well before it can attain its full moment capacity. Such
type of beams are known as Laterally Unsupported Beams.

6. Tension Members:
Primarily occur as:
1. Chord Members in trusses
2. In diagonal bracing in bracing systems
3. Cable elements in suspension roofs , main cables of
suspension bridges and suspenders.
Compression Members
Primarily Occur as:
Columns in buildings;
Chord Members in trusses and diagonal members in end
panels of trusses
Stability is an important consideration in design and behavior
of compression members Area is generally spread out to
maximize Radius of Gyration

7. Fire Protection For Steel Structures
Passive fire protection materials insulate steel structures from the effects of the high temperatures that may
be generated in fire. They can be divided into two types, non-reactive, of which the most common types are
boards and sprays, and reactive, of which thin film intumescent coatings are the most common example.
Thin film intumescent coatings can be either on-site or off-site applied. Intumescent coatings are paint like
materials which are inert at low temperatures but which provide insulation as a result of a complex chemical
reaction at temperatures typically of about 200-250°C. At these temperatures the properties of steel will not
be affected. They are mainly used in buildings where the fire resistance requirements are 30, 60 and 90
minutes.
In recent years, a number of products have been developed which can provide 120 minutes fire resistance .
They can be applied either on-site or off-site.
In general, most on-site application is carried out using water based materials.
Boards are widely used for structural fire protection. They are used both where the protection system is in full
view and where it is hidden. They offer the specifier a clean, boxed appearance and have the additional
advantages that application is a dry trade and may not have significant impacts on other activities. Also,
boards are factory manufactured and thicknesses can be guaranteed. Furthermore, boards can be applied on
unpainted steelwork.
Spray protection is extensively used in the United States but is less common in the United Kingdom. It has the
advantage that it can be used to cover complex shapes and details and also that costs do not increase
significantly with increases in protection thickness. This is because much of the cost of application is in the
labour and equipment and a minority is in the cost of the material.
Flexible fire protection systems have been developed as a response to the need for an easily applied fire
protection material which can be used on complex shapes and details but where application is a dry trade.
There are a limited number of manufacturers of these products.

8. ADVANTAGES AND DISADVANTAGES OF BOLTED CONNECTIONS
Some advantages of bolted joints:
1) They are easily disassembled, as opposed to something like riveting or welding, which requires
cutting.
2) They can be designed to take tension loads, unlike riveting (by tightening the bolt/nut to
develop a preload, you reduce the effects of fatigue due to cyclic loading, which you can't do with
a rivet; plus, rivets can easily pull through a hole when loaded in tension).
3) Welds require heating a metal, which can change the properties in the heat-affected zone, and
can also create thermal stresses. Bolts avoid this problem. You're also not likely to start a fire
(welds) or breathe toxic fumes (welds and adhesive joints) when you're installing a bolt.
4) Bolted joints aren't particularly sensitive to the condition of the parent material. With welds
and adhesive joints, the parent material needs to be clean, free of oils, etc (and obviously, it has
to be metal to weld).
5) You can put a bolt in a blind hole (one that doesn't go all the way through the material); you
can't use a rivet.
6) Bolts are easy. Welding takes a lot of skill and a lot of time, particularly if you're going to
inspect the weld for flaws after it's completed. But just about everybody has used a wrench.
7) Bolts offer much better joint quality than a screw, mostly because the threads are more tightly
controlled.

9. Some disadvantages:
1) They require access to both sides of the joint (although this can be overcome using studs or special bolts like Hi-Loks). Welding,
adhesive joints, and some types of riveting can be done with access to only one side of the joint.
2) They can become loose over time as the nut backs off (this can be addressed to some extent by using the proper preload and
thread-locking features) or as the material creeps. Welding and adhesive joints don't have this problem.
3) They require holes, which introduce stress concentrations and more failure modes; drilling the holes may create cracks which
will grow over time to cause failure. Welding and adhesive joints don't require holes. Also, welds and adhesive joints are
continuous, so they don't concentrate load like a bolt does.
4) Preload can be tough to measure accurately - it depends on the method of tightening, the friction between the threads of the
bolt and the nut, etc.
5) Complexity. A bolted joint adds to a part count - a bolt, a nut, washers, thread lubricant, thread locking compound. And the
bolts, nuts, and washers come in specific sizes with specific threads, with specific hole sizes and tolerances, for specific
applications - if you need a high quality joint, you've got to keep track of all that and make sure the right bolt is used in the right
place and in the right way.
6) Damage to a threaded hole is tough to replace - you can drill it out and rethread, but using a larger bolt might change your load
distribution. To avoid that, you can use an insert in the parent material - basically a tube that is threaded on the outside and on
the inside, but that adds complexity. (Of course, all this is related to the advantage of actually being able to disassemble and
reassemble a bolted joint, so you might not actually call it a disadvantage compared to other fastening processes.)
7) Corrosion between a bolt and the parent material should be considered. This may not be a problem with welding and adhesive
joints if the parent materials being welded are compatible.
8) Bolted joints require a gasket to seal a joint. A weld (if done properly) will be leak-proof.
9) Bolted joints aren't so easy after all - I know of robots that weld, but the manual dexterity needed to install a bolt still requires a
human touch.

11. BRACKETT CONNECTIONS
Brackets are projections that carry loads.
The connection of a bracket to a support has to transmit both shear and
moment.
Fasteners or welds may be used for the purpose. Connections may be made
with fasteners or welds subjected only to shear or to combined shear and
tension.
Each fastener is subjected to a shear load and a load due to moment.
The load due to moment on any fastener acts normal to the radius vector
from the center of gravity O of the fastener group to the fastener.The
resultant of this load and the shear load must be less than the allowable
capacity of the fastener.
• connection is satisfactory.
• An ultimate-strength method that gives an accurate estimate of the
strength of eccentrically loaded bolt groups.
• The method assumes
that fastener groups rotate about an instantaneous center.

12. DEFINITIONS
Pitch of the bolt/ screw thread:
A screw thread, often shortened to thread, is a helical structure used to convert between rotational
and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the
form of a helix, with the former being called a straight thread and the latter called a tapered thread.
A screw thread is the essential feature of the screw as a simple machine and also as a fastener.
The mechanical advantage of a screw thread depends on its lead, which is the linear distance the
screw travels in one revolution.
1. Pitch of the Bolts (p): It is the centre-to-centre spacing of the bolts in a row, measured along the
direction of load.
2. Gauge Distance (g): It is the distance between the two consecutive bolts of adjacent rows and is
measured at right angles to the direction of load.
3. Edge Distance (e): It is the distance of bolt hole from the adjacent edge of the plate.