Armo. Structurally sound even in an earthquake.

SIA 266 Standard

The revised SIA 266 standard substantially clarifies the verification of earthquake resistance for masonry buildings. Compared to the previous standard, the slenderness condition for shear walls no longer applies; instead, stresses must be verified both in the plane of the wall and transverse to it. The behaviour factor q is determined based on the normal force stress or the deformation capacity. In addition, a deformation-based method may be applied.

• Verification in-plane and transverse to the wall
• Behaviour factor q = 1.5 when activating all load-bearing masonry walls
• Behaviour factor q = 2.0 for shear walls with the Seismur wall system
• Deformation-based verification permitted
• Masonry with thin-bed mortar joints is considered standard masonry if minimum strengths are met

Shear stress with centric normal force

Structural safety under shear stress is considered verified if the compressive strength is not exceeded at any point. Inclined compressive stresses up to fαd may be superimposed with compressive stresses acting perpendicular to the bed joints up to fxd − fαd. The simple or extended verification must be carried out per SIA 266.

Seismur Wall System

The Seismur wall system turns an unreinforced masonry wall into masonry with tension elements. Prestressed wall elements at the wall ends form the tension elements; the tensile forces are also anchored in the floor slabs. Floor slabs and wall elements form a frame within which the masonry is enclosed. The masonry can develop a compressive stress field independently of the normal force stress — behaviour factor q = 2.0 is thus permissible.

The shear resistance of Seismur walls is limited by three mechanisms:

A limit on shear resistance is given by the maximum inclination angle of 31° due to joint shearing. As wall utilisation with respect to normal force increases, shear capacity decreases — relevant mainly for short walls.

Calculation Methods

Three complementary methods are available for verifying earthquake resistance. All allow a substantially better computational utilisation of the existing earthquake resistance than conventional linear-elastic calculation.

Case Study: Multi-Family House in Lyss

A 4-storey multi-family house (4th floor as attic storey) in seismic zone Z1, ground class E, building class I. Reinforced concrete floor slabs, 26 cm thick. Masonry walls 15 and 17.5 cm wide.

Conclusion: the macro-element calculation (3muri) resulted in a compliance factor of 1.20/0.70 = 1.71. The deformation-based calculation accounts for individual deformation capacity and typically yields the most favourable results.

Seismic Zones of Switzerland

Switzerland is divided into four seismic zones (SIA 261). Masonry per SIA 266 is suitable for all zones; the choice of construction system and behaviour factor depends on zone, ground class and building class.

ARMO Formats

Advantages of Masonry in an Earthquake

• High compressive strength allows slender, material-saving wall cross-sections
• Non-combustible materials — no toxic smoke in case of fire
• Mass and stiffness of the masonry dampen vibrations
• Long service life and high resale value of the building
• Local raw materials, short transport distances, complete cycles