undefined | unit 3 tension members

DSS

Unit – 3

Tension members

Q1) Write a short note on tension members.

A1) Tension members are structural elements which are subjected to axial tensile forces. Examples of anxiety members are bracing for homes and bridges, truss members, and cables in suspended roof systems.

In an axially loaded anxiety member, the strain is given by:

F = P/A

Where in P is the importance of the burden and A is the pass-sectional place.

Q2) Describe design of tension members.

A2) To layout anxiety members, it is crucial to examine how the member might fail beneath Neath each yielding (excessive deformation) and fracture, which can be taken into consideration the restriction states. The restriction nation that produces the smallest layout energy is taken into consideration the controlling restriction nation. It additionally prevents the shape from failure.

Using American Institute of Steel Construction standards, the last load on a shape may be calculated from one of the following combination:

1.4 D

1.2 D + 1.6 L + 0.5 (Lr or S)

1.2 D + 1.6 (Lr or S) + (0.5 L or 0.8 W)

1.2 D + 1.6 W + 0.5 L + 0.5 (Lr or S)

0.9 D + 1.6 W

L= 14

D… is the dead load or the weight of the structure itself

L… is the live load which vary for different structures

S… is the snow load

W… is the wind load

Q3) Explain step wise design of tension member.

A3)

1. Corresponding to the loading on the shape of which the anxiety member is a part, the tensile pressure withinside the member is first computed.

2. The internet vicinity required for the member is decided via way of means of dividing the tensile pressure withinside the member via way of means of the permissible tensile pressure.

3. Now, an appropriate phase having gross vicinity approximately 20 in step with cent to twenty-five in step with cent extra than the predicted vicinity is decided on. For the member decided on deductions are made for the vicinity of rivet holes and the internet powerful vicinity of the phase is decided. If the internet vicinity of the phase of the member so decided is extra than the internet vicinity requirement predicted in step i, the layout is taken into consideration safe.

4. The slenderness ratio of an anxiety member shall now no longer exceed 400. In the case of an anxiety member vulnerable to reversal of pressure because of the motion of wind or earthquake, slenderness ratio shall now no longer exceed 350. If the reversal of pressure is because of masses others than wind or earthquake, the slenderness ratio shall now no longer exceed 180.

Q4) Give maximum values of slenderness ratio.

A4)

A tension member in which a reversal of direct stress occurs due to loads other than wind or seismic forces = 180

A member subjected to compressive forces resulting only from a combination of wind earthquake actions, provided the deformation of such a member does not adversely affect the stresses in any part of the structure = 250

A member normally acting as a tie in a roof truss or a bracing member, which is not considered effective when subject to reversal of stress resulting from the action of wind or earthquake forces = 350

Q5) Explain displacement of tension members.

A5) The increase in the length of a member due to axial tension under service loads is

A = PL/(EAg)

where is the axial elongation of the member (mm),

P is the axial tensile force (un-factored) in the member (N),

L is the length of the member (mm), and

E is the modulus of elasticity of steel = 2.0 x lo5 MPa

Q6) What is shear lag?

A6)

The tensile pressure to an anxiety member is transferred via way of means of a gusset plate or via way of means of the adjoining member linked to one of the legs both via way of means of bolting or welding.

This pressure that's transferred to at least one leg via way of means of the cease connection regionally gets transferred as tensile pressure over the whole move segment via way of means of shear.

Hence, the distribution of tensile pressure at the segment from the primary bolt hollow to the ultimate bolt hollow will now no longer be uniform. Hence, the linked leg will have better stresses at failure even as the stresses withinside the superb leg might be noticeably lower.

However, at sections some distance far from the cease connection, the pressure distribution turns into extra uniform. Here the pressure switch mechanism, i.e., the inner switch of forces from one leg to the other (or flange to web, or from one component to the other), other), might be via way of means of shear and due to the fact due to the fact one component ‘lags’ at the back of the other, the phenomenon is cited as ‘shear lag’. The shear lag reduces the effectiveness of the issue plates of an anxiety member that aren't linked without delay to a gusset plate.

Q7) State modes of failure of tension members.

A7) The extraordinary modes of failure in anxiety contributors are

1. Gross segment yielding

2. Net segment rupture

3. Block shear failure

Q8) Explain factors that effect on shear lag.

A8)

1. The thickness of the member does not play a role in the determination of shear lag factor or it does not affect the tensile capacity of the section.

2. If the distance between the plane of connection and the centroidal axis of the outstanding leg increases, it reduces the tension capacity of the section.

3. From the experimental studies, it is proved that if the length of the connection is increased up to 4 bolts, the tensile capacity increases. And if we further increase the length, it does not have a significant effect. (Kulak and Wu, 1997).

Q9) What is called as lug angles?

A9) Lug angles are sometimes used to reduce the length of connections. Figure below shows the lug angle connection with single or a channel type of tension member.

Due to the possible deformation of the outstanding leg of the lug angle, the rivets connecting the gusset plate with the lug angle will share less load than the rivets connecting the main member with the gusset plate.

Q10) what is compression members?

A10)

Compression contributors are structural factors which can be driven collectively or bring a load, extra technically they're subjected best to axial compressive forces.

That is, the masses are implemented at the longitudinal axis via the centroid of the member pass segment, and the load over the pass sectional place offers the pressure at the compressed member.

In homes, posts and columns are nearly continually compression contributors as are the top chord of trusses.

A structural member loaded axially in compression is normally referred to as a compression member.

Vertical compression contributors in homes are referred to as columns, posts or stanchions. A compression member in roof trusses is referred to as struts and in a crane is referred to as a boom.

Q11) Enlist types of column bases.

A11)

(i) Slab base

(ii) Gusseted base

(i) Slab Base:

In this association the column stands at once over a metal base plate which rests over a concrete basis. The base plate is attached to the column flanges with connecting angles with the aid of using welding or bolting. The column-base plate unit is geared up withinside the concrete basis with basis bolts.

(ii) Gusseted Base:

Gusseted base plates are used for columns sporting heavy loads. In this example fastenings are used to connect the bottom plate and the column withinside the shape of gusset plates, angles etc.

Compression contributors of roof trusses are composed of unmarried angles or double angles. These contributors can be non-stop contributors (just like the fundamental rafter of the roof truss) or discontinuous contributors (just like the vertical and diagonal contributors of the truss).

Q12) What is single angle strut?

A12) The compressive pressure in unmarried perspective can be transferred both concentrically to its centroid via cease gusset or eccentrically with the aid of using connecting one in all its legs to a gusset or adjacent member.

Q13) Write short note on Strength of compression member.

A13)

The power of a compression member is described as its secure load sporting potential.

The power of a centrally loaded immediately metal column relies upon at the powerful cross-sectional place, radius of gyration (viz., form of the cross-phase), the powerful duration, the importance and distribution of residual stresses, annealing, out of straightness and bloodless straightening.

The powerful cross-sectional place and the slenderness ratio of the compression contributors are the primary features, which have an effect on its power

Q14) What are continuous members?

A14)

The compression members (consisting of single or double angles) which are continuous over a number of joints are known as continuous members.

The top chord members of truss girders and principal rafters of roof trusses are continuous members.

The effective length of such compression members is adopted between 0.7 and 1.0 times the distance between the centers of intersections, depending upon degree of restraint provided. When the members of trusses buckle in the plane perpendicular to the plane of the truss, the effective length shall be taken as 1.0 times the distance between the points of restraint.

The working stresses for such compression members is adopted from IS:800-1984 corresponding to the slenderness ratio of the member and yield stress for steel.

Q15) What is Discontinuous members?

A15)

The compression members which are not continuous over a number of joints, i.e., which extend between two adjacent joints only are known as discontinuous members.

The discontinuous members may consist of single angle strut or double angle strut.

When an angle strut is connected to a gusset plate or to any structural member by one leg, the load transmitted through the strut, is eccentric on the section of the strut.

As a result of this, bending stress is developed along with direct stress.

Q16) Explain Double Angle Strut.

A16)

A double angle discontinuous strut with angles placed back-to-back and connected to both sides of a gusset or any rolled steel section by not less than two rivets or bolts or in line along the angles at each end or by equivalent in welding as shown in Fig. 11.3.A, can be regarded as an axially loaded strut. Its effective length is adopted as 0.85 times the distance between intersections, depending on the degree of restraint provided and in the plane perpendicular to that of the gusset, the effective length ‘l’ shall be taken as equal to the distance between centers of the intersections. The tacking rivets should be provided at appropriate pitch.

The double angles, back-to-back connected to one side of a gusset plate or a section by one or more rivets or bolts or welds as show in Fig. 11.3.B, these are designed as single angle discontinuous strut connected by single rivet or bolt.

If the struts carry in addition to axial loads, loads which cause transverse bending, the combined bending and axial stress shall be checked as described for the columns subjected to eccentric loading. The tacking rivets should be provided at appropriate pitch.

Q17) Explain Gussets.

A17)

A gusset plate is a plate provided at the ends of tension members through which the forces are transferred to the main member.

Gusset plates may be used to join more than one member at a joint. The lines of action of truss members meeting at a joint should coincide.

If they do not coincide, secondary bending moments and stresses are created, which should be considered in the design.

The size and shape of the gusset plates are decided based on the direction of various members meeting at a joint. The plate outlines are fixed so as to meet the minimum edge distances specified for the bolts that are used to connect the various members at a particular joint.

The shape of the gusset plate should be such that it should give an aesthetic appearance, in addition to meeting the edge distances of bolts, as mentioned earlier.

Q18) What is the net area A, for the tension member shown in Fig., in case of (a) drilled holes, (3) punched holes?

A18)

Ag = 100 x 10 = 1000 mm2

(a) Hole made by drilling Hole for M20 bolt = 22 mm

(b) Ag =Ag - n (hole x thickness of plate) = 1000 - 2 (22 x 10) = 560 mm2 (6) Holes made by punching Hole = 22 + 2 = 24 mm

Q19) Write short note on Effective length of compression member.

A19)

(a) The effect of end restraints on column strength is usually incorporated in the design by the concept of effective length. (It must be emphasized that the concept of effective length is only a simple and convenient short cut and the designer is not obliged to use it, if helshe knows a better, yet sufficiently simple solution.)

(b) Hence, in this section the effective length concept is first explained for idealized boundary conditions and then extended to cases where intermediate restraints are present.

(d) Note that Wood’s Curves (used in British and Indian codes), which are used to determine the effective length of columns of multi-story buildings are also explained.

Q20) Write note on built up compression members.

A20) For large loads and for efficient use of material, built-up columns (also called as combined columns or open-web columns) are often used.

They are generally made up of two or more individual sections such as angles, channels, or I-sections and properly connected along their length by lacing or battening so that they act together as a single unit. Such laced combined compression members are often used in bridge trusses. According to the type of connection between the chords, built-up members may be classified as follows:

Laced members

Struts with batten plates

Battened struts

Members with perforated cover plates

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