Lattice girders

Lattice supports, made of longitudinal ribbed cold-drawn steel bars B500A, nominal diameter 6mm and 7mm, are connected to each other by diagonal smooth cold-drawn steel bars B500A, nominal diameter 4.2mm. Lattice supports are made in accordance with the requirements of the Regulation on technical and other requirements for steel for concrete reinforcement (Official Gazette of the RS, no. 35/2015 and 44/2016) and the SRPS EN 10080:2008 standard.

Lattice supports are used for mezzanine and roof structures in high-rise buildings.

The standard dimensions of the lattice supports are shown in Table 1. According to the customer’s request, deviations are possible in the height H (up to 300 mm) and the length of the lattice support L (less than 12000 mm).

Table 1. Standard dimensions of lattice supports

Figure 1. Geometric characteristics of lattice supports

Permissible deviations for trusses are:

Ribbed steel wire is characterized by the dimensions, number and configuration of the ribs. Ribbed steel wire has three rows of transverse ribs that are evenly spaced around the circumference. The values ​​of the height of the ribs, their mutual distance, inclination in relation to the longitudinal axis, and the sum of the distances are given in Table 1 and are shown in Figure 2.

Figure 2 Rib configuration

Table 1. Limits for rib parameters

Lattice supports are made of cold-drawn ribbed wire of technical grade B500A, with the following mechanical characteristics:

– Conventional yield stress minimum Rp0.2 = 500 N/mm2
– The ratio of tensile strength to conventional yield stress, Rm/Rp0.2 must be greater than 1.02 (for wire diameters less than 8 mm).
– The total elongation Agt at the highest force must be 1 %, (for wire diameters less than 8 mm).

Shear force of welded joints in welded mesh:
Fw > 3.53 kN, for trusses with 6 mm diameter bars
Fw > 4.81 kN, for trusses with 7 mm diameter bars,

according to the formula: Fw > 0.25 × ReCh × ACh where ReCh is the yield stress of the bar in the lattice support, and ACh is the cross-sectional area of ​​the longitudinal bar at the joint in the lattice support.

Weldability is determined by two characteristics:

1) carbon equivalent;
2) by limiting the content of certain elements.

The highest values ​​of individual elements that enter the chemical composition of steel for reinforcing concrete and the carbon equivalent must not exceed the values ​​given in Table 2, and in accordance with the standard SRPS EN 10080, point 7.1.2.
Table 2. Chemical composition (% mass)

The carbon equivalent value Ceq is calculated according to the formula:

Ceq= C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

where the content of chemical elements is expressed in % mass.