CURS 4

3. Fundamental types of structural systems for buildings. Problems refering to the geometry of plan and of volume of buildings

The most known structural type for buildings is the structural walls system for which the Structure subsystem is formed by vertical walls, exterior and interior, disposed after two orthogonal directions. This system is called Honeycomb system and it confers structural rigidity and a good capacity to the action of horizontal forces. It has the disadvantage of freezing the architectural lay out. The distances between two successive structural walls are small- 3-6 m, each slab being solved without intermediate beams. The exterior walls must be thermal-insulated. As construction materials: bricks,reinfored concrete or precast panels may be used

Structural walls system honeycomb system

Another variant of structural system with structural walls is the one in which these are disposed in cellular system, meaning at greater distances one with repect to the other, such that the walls will border not only a room but an ensemble of indoor spaces. This system improves the functional architectural flexibility, trying to decrease the effect of lay-out freezing.

The rigidity of the frame structure of a cellular system with respect to the ensemble rigidity to horizontal forces is much less than that of the diaphragms, in many situations the frames are considered to transmitt only vertical forces and are called gravitational frames.

CELLULAR SYSTEM of aStructural walls system

Another type of structure formed by vertical and horizontal structural elements (bar type) rigidly jointed, is known as the frame structure (or with skeleton).Each column belongs simultaneously to two plane frames: transversal and longitudinal.Each plane frame is dimensioned to carry over the gravitational forces and the horizontal forces as part of the spatial system. This type of system permits the architectural flexibility, the partitions are nonstructural and discharging on slabs The frame structural systems are much more deformable under the action of horizontal forces than one with structural walls, which can lead, in the case of an severe earthquake, to difficult repairable degradations of partition walls or closure walls.

Frame structuresInterior and closure walls are non structuralOffers increased flexibility

A solution combining the advantages of indoor flexibility ( frames) with the advantage of moderate flexibility to horizontal forces ( walls) is the dual structure.Such a structural system associates an ensemble of frames to a number of structural walls disposed independent or notTo such structural systems, the general rigidity of frames to horizontal forces is enhanced by the structural walls, and inversely, the increased structural rigidity of walls is well-balanced by the present of the frame elements. The dual structures are conceived and dimensioned to carry over gravitational and horizontal forces, both systems working together in this sense. The system is utilized to high and very high rise buildings.

Dual structure withnot-coupled walls (independent)

Dual structure with grouped structural walls (central core)

Fundamental types of structural systems defined according to Romanian code P100/2013 Reinforced concrete structures may be classified in the following fundamental types, according to the estimate behavior under horizontal seismic loads:frame systemdual system (mainly working with frames or walls); structural wall system;inverted pendulum system;flexible in torsion system;Frame structural system: structural system for which the seismic loads are carried over more than 70% only by spatial frames .

Structural wall system: The structural system for which the vertical walls, coupled or not, are carrying over most of the vertical and horizontal loads and whose capacity at lateral loads action is at least 70% of the entire structural system. In other words, this system is designed to take over at least 70% of the design lateral load.

Dual structural system: The structural system for which vertical loads are mainly carried by spatial frames , and the lateral loads are carried partially by the spatial frames, partially by structural independent or coupled structural walls.This system comes into two solutions:

Dual system with structural walls mainly working: the contribution of structural walls in taking over lateral loads is at least 50% from the totalDual system with frames mainly working: the contribution of frames in taking over lateral loads is at least 50% from the total

System flexible in torsion: In this category dual and structural wall systems sensible to torsion are included (ex: the system with central core)

Inverted pendulum system: The system for which more than 50 % of its mass is concentrated in the upper third or for which the energy dissipation mechanism is mainly concentrated at the base of one element.