Deformations of temporary wooden supports used to reduce building deflections in mining areas

Abstract

Temporary supports, consisting of a stack of wooden elements and a hydraulic jack, are used in the process of removing deflections in buildings with one to three aboveground floors in mining areas. During uneven raising, the supports are loaded monotonically, unloaded and loaded cyclically. Laboratory tests were designed for the supports. For the investigated range of loads of 0 to 400 kN, under a growing load, a linear relationship exists between a load and the change in the stack length, which signifies that the deformations of wooden elements and displacements related to their mutual interactions increase proportionally. A seemingly higher stack stiffness is seen at the beginning of the unloading process and for cyclical loads, meaning that in this phase of loading, the material deformation of the wooden elements and the jack is responsible for changing the jack length in this load phase, with a negligible presence of mutual displacements of wooden elements. The support, after being unloaded, returns to the initial position and its permanent deformations are not observed. The stiffness of a temporary support decreases as the height of the stack of wooden elements increases.

Effect of Eccentricity of Applied Force and Geometrical Imperfections on Stiffness of Stack of Cuboidal Steel Elements

“…Hence, a considerable decline of the value Q at a relatively small change in the displacement u occurred. The part of the relationship Q-u, at which the load Q decreased by the value ΔQ was Phase II of loading, for which the load ΔQ was determined from (24). When the load value was reduced by ΔQ = 2Nint,fr(uint,max), the sense of the friction force changed.…”

“…There are few tests on supports composed of the jack and a stack of cuboidal elements. However, they only referred to axially compressed supports of stacks made of cuboidal wooden [ 24 ] and steel [ 25 ] elements. Moreover, such supports examined in situ [ 26 ] showed their stiffness has a decisive impact on parameters of a rectified building.…”

Examination of stiffness of stack of steel elements forming part of supports used for removal of building deflections

“…Subject to investigations up till now have been only the parameters of a stack of wooden elements used for elimination of defl ections of low structures, with up to three stories (Gromysz, 2018). Moreover, the analyses of axially and eccentrically loaded elements have been carried out mainly in relation to reinforced concrete elements (Kabir & Shafei, 2012), steel columns (Nie, Kang, Shen & Yang, 2017) and masonry structures (Bernat--Maso, Gil & Roca, 2015;Moradabadi, Laefer, Clarke & Lourenço, 2015).…”

Stiffness test in lateral direction of temporary wooden building supports

“…The changes are caused by temporary and cyclic loads of stacks of wooden elements (the underpinning) by jacks. This issue was a subject of the laboratory tests discussed in [2]. Displacements in the horizontal direction occur because supports transmit a horizontal force designated as Qx.…”