A joint of lattice aluminium welded structure made of circular hollow sections (CHS) has been analysed. Aluminium alloy EN AW 6082-T6 was used. Calculation of ultimate load bearing capacity of lattice structure web member assumes check of element load bearing capacity for the following calculation situations:- calculation of ultimate load bearing capacity of compressed elements with the influence of buckling,- calculation of ultimate load bearing capacity of compressed elements with the influence of HAZ,- calculation of ultimate load bearing capacity of tensioned elements with the influence of HAZ,- calculation of ultimate element force in truss joint, depending on joint construction.The first three checks are independent of type and characteristics of truss chords. They depend only on elements connection manner and geometrical characteristics of web members. The fourth condition directly depends on relation of chord and web member characteristics, i.e. ratio of their diameters and tube wall thicknesses. The choice of joint geometry, gap between elements in joint as well as joint eccentricity are also important for ultimate force in web member. Check of K-joint ultimate bearing capacity is particularly needed for welded joints due to aluminium strength decrease caused by HAZ (Heat Affected Zone) effect.European standard EN 1999 for aluminium structures design has not defined ultimate load of web members regarding type and characteristics of joint connection.Value of ultimate force in web member of K-joint, depending on connection type, by means of expressions defined in EN 1993-1-8 (Design of steel structures - Part 1-8: Design of joints), has been analysed. Comparative analysis has been done by means of ANSYS modelling, taking into consideration real characteristics of aluminium alloy and ultimate load bearing capacity reduction in the vicinity of weld due to HAZ effect. The main goal of the paper is to analyse capability of expressions from EN 1993-1-8 for steel structures to be used in aluminium structures, having in mind quoted limitations.