Lassing and Battering system

ESD steel portion.

1. GANDHINAGAR INSTITUTE OF TECHNOLOGY BE S EM :-6 th DEPARTMENT OF CIVIL ENGINERING Active Learning Assignment of ELEMENTARY STRUCTURAL DESING (STEEL) Topic : LASSING AND BATTERING SYSTEM Prepared By: PRAJAPATI HIMANSU 140120106085 Guided By Prof. Mohammed Challawala

2. Introduction Typical joining of the components is done by two ways Lacing Battening Lacing bars or battern plates are not design as load carrying members. They carry transverse shear force which occurs when the column defects.

3. Lacing

4. There are two types of lacing system. Single lacing system Double lacing system The lacing system should not be varied throughout the length of the strut as far as practicable.

5. The single-laced systems on opposite sides of the main components should preferably be in the same direction so that one system is the shadow of the other. Cross (except tie plates) should not be provided along the length of the column with lacing system, unless all forces resulting from deformation of column members are calculated and provided for in the lacing and its fastening.

6. DESIGN REQUIREMENT FOR LACING (AS PER IS : 800 – 2007 CL. 7.6 PG. NO.48 )

7. (1) Angle of inclination( θ ): (cl. 7.6.4) For single or double lacing system, θ = 40 ͦ to 70 ͦ To the axis of the built up member normally,=45 is taken (2) Slendernes ratio( kL /r) : (cl. 7.6.5.1) KL/r for each component of column, should not be greater than 50. ( or) kL /r not greater than 0.7 *most favourable slenderness ratio of the member as a whole

8. The slenderness ratio of lacing shall not exceed 145 (cl.7.6.6.3) (3) Effective length of lacing (le) : For bolted connection : For single lacing, le = L For double lacing, le = 0.7 l Where, L = distance between the inner end fastner For welded connection : Le = 0.7 x distance between the inner ends of welds

9. (4) Width of lacing bars(b) : ( cl , 7.6.2) minimum width of lacing bar, b = 3d Wh, D = nominal diameter of bolt ( 5) Thickness of lacing (t) : (cl. 7.6.3) For single lacing, t > Le/40 For double lacing, t > Le/60

10. (6) Transverse shear ( Vt ) : (cl. 7.6.6.1) Vt = 2.5% of the axial force in the column. This force shall be divided equally among the lacing systems in parallel Planes. For single lacing F= Vt / 2sin ϴ For double lacing F= Vt /4 sin ϴ wh, F= axial force in each lacing bar

11. (7) Check for compressive strength For lacing using Le/r min & fy = 250 Mpa Find fcd from IS: 800, table -9 (c) pg. 42 For rectangular section buckling class is “c”. So, Compressive load carrying capacity of lacing Pd = (b x t) x fcd If (b x t ) x fcd > F (axial force n lacing) …. OK b*t = area of lacing i.e. pd > F …. OK

12. (8) Check for Tensile Strength Tensile strength of lacing flat is, Or Whichever is less. If …O.K. IS : 800 cl. 6.3.1, pg 32

13. (9) End connections : The bolted connection for lacing may be two types as given case. For case (a) Resultant force on bolt = R = F So, no of bolts required

14. For case (b) Resultant force on bolt So No. of bolts required Strength in single shear 16 dia. Bolts = 29 kN 20 dia. Bolts = 45.3 kN

15. Strength of bolt in bearing (cl. 10.3.4) (10) Overlap In case of welded connection, the amount of overlap measured along either edge of lacing bar shall not be less than , four times the thickness of the lacing bar (or) The thickness of the element of main member, whichever is less.

16. Battening

17. Compression member can also be built up intermediate horizontal connecting plates or angle connecting two or four elements of column .these horizontal connecting plates are called battens. The number of battens shall be such that the member is divided into not less than three bays within its actual length

18. DESIGN REQUIREMENT FOR BATTENING (AS PER IS : 800 – 2007 CL. 7.6 PG. NO.51 )

19. (1) The number of battens shall be such that the member is divided into not less than three bays. (2) Battens shall be designed to resist simultaneous

20. Longitudinal shear Vb = Vt C / Ns Moment M= Vt C / 2N Where, Vt = transverse shear force C = distance between centre to centre of battens longitudinally . N = number of parallel planes of battens (2 usually) S = Minimum transverse distance between the centroid of the bolt/ rivet group / welding.

21. (3) Slenderness Ratio : (cl. 7.7.1.4) The effective slenderness ratio of battened column shall be taken as 1.1 times the ,the maximum actual slenderness ratio of the column, to account for shear deformation effects. (4) Spacing of battens (C) : (cl. 7.7.3) For any component of column, (1) (2) of built up column (which ever is smaller)

22. (5) Thickness of battens (t) : (cl. 7.7.2.3) wh, = distance b/w the inner most connecting lines of bolts, perpendicular to the main member (6) Effective Depth of battens (de) : ( cl 7.7.2.3) de > 3/4 * a …for intermediate battens de > a ,……. ...For end batten de > 2b , …… For any battens Wh, de = distance between outermost bolts longitudinally a = distance between centroids of the main member b = width of one member

23. Overall depth of battens D = de + (2 * end distance) (7) Transverse shear ( Vt ) : (cl. 7.7.2.1) Vt = 2.5 % of the factored axial column load (8) Overlap (cl. 7.7.4.1) for welded connection, the overlap shall be not less than four times the thickness of the battens It should be noted that the battens columns have least resistance to shear compared to column with lacings