The invention relates to a modular HD (Heavy Duty) support system (1) having a strongly increased resistance to breaking strain and strain of flexure for the support of very huge and heavy shuttering for use in modern building. This module comprises vertical upright assembly systems (2) consisting of upright elements (2′) with connecting members (3) and intermediate frames (5). The bottom part and/or top part of each upright assembly (2) is provided with a spindle assembly (4), which is capable of carrying a high load and with adjustable butterfly nuts (20) and coupling pieces (21). In upward direction the upright assembly systems (2) are extended by means of connecting pieces (3) provided with locking pins (8a, 8b) for obtaining a connection which is resistant to tensile strain. In lateral direction the upright assembly systems (2) are intercoupled by means of a coupling assembly comprising a screw member (46) and claws (47, 48) positioned on intermediate frames (5) and also C-shaped coupling members positioned on upright elements (2′), but also on a coupling piece (21) of a spindle assembly (4) for reducing the flexing length thereof. The module (1) is transportable as a whole in assembled position and even in height adjustable under load. The module (1) may be in height and also in width and in length be extended moreover by practically an unlimited number of upright assembly systems (2) and intermediate frames (5).