PSI - Issue 78

Christoph Butenweg et al. / Procedia Structural Integrity 78 (2026) 1689–1696

1692

of strength class C30/37 and ductile B500B reinforcing steel. Columns were designed as 25/25 cm squares, while beams had rectangular sections of 25/45 cm. The masonry infills were constructed using Thermoplan SX10 clay bricks (Bellenberg, 2025) representing modern, highly thermally insulating bricks with a thickness of 300 mm. More detailed information regarding reinforcement arrangement and material characteristics for bricks, mortar, and masonry are given in Milijaš et al. (2023, 2024). At the start of the test, two one-way hydraulic actuators on each side apply a constant vertical load of 200 kN per column, simulating the axial load of an external frame in a representative five-storey building. This load remains constant throughout the test. Horizontal in-plane loading is displacement-controlled using a sinusoidal load function, applied stepwise with three cycles at each displacement level. Displacements gradually increase up to a maximum interstorey drift with respect to the storey height of 2.75 m. Out-of-plane loading is applied using four airbags in cyclic loading and unloading phases. In simultaneous loading tests in-plane and out-of-plane loads are simultaneously applied. The out-of-plane load levels are applied to fulfil or exceed the seismic demand requirements of EN 1998-1 (2004).

Major strains and damage pattern for decoupled infills

Major strains and damage pattern for traditional infills

Load displacement curves

300

Test T3 Test D3

200

100

0

-3,0

-2,0

-1,0

0,0

1,0

2,0

3,0

-100

Base shear [kN]

-200

-300

Drift [%]

T3 - IPD: 1,4%

D3 - IPD: 2,5%

T6 – IPD: 1,4%

D6 - IPD: 2,5%

T9 - IPD: 1,0%

D9 - IPD: 2,5%

Fig. 3. Comparison: Cyclic load-displacement curves and major strains with damage pattern for traditional and decoupled infills.

3.1.4 Comparison of results and findings The effectiveness of decoupling masonry infills from the reinforced concrete frame is assessed by comparing the cyclic load-deformation curves between frames with traditional infills (T3, T6, T9) and decoupled infills (D3, D6, D9), as well as by comparing the damage patterns corresponding to the maximum interstory drifts reached. Fig. 3 visually illustrates the comparison of hysteretic curves for the three configurations of traditional and decoupled infills. A comparison of the load-deformation curves shows that masonry infills with decoupling reach drift values of up to 2.5% under simultaneous in-plane and out-of-plane loading without sustaining significant damage. The applied loading function in both directions fully cover the combinations of seismic actions according to the 30% rule