Earthquake-Resistant Construction with Porotherm Clay Block


The design philosophy for clay block is a system consisting of aerated fired clay blocks, designation R25Th+, nominally 500mm long x 250mm thick x 249mm high, stretcher bonded, using a thin-bed mortar joint proprietary system, 1mm thick, in accordance with DIN 1053-1, Z17.1-628, EN 998-2.

Masonry calculations are in accordance with Eurocode 8 BS EN 1998 -1:2004 Design of Structures for Earthquake Resistance which refers to and uses Eurocode 6 BS EN 1996 – 1:2005. General Rules for Reinforced Masonry Structures and 1996 – 3:2006. It is recommended construction monitoring to level CM3 or better is carried out by a registered structural engineer.

The basis of the design is Confined Masonry Construction (CMC) in accordance with the Eurocodes as stated above. The 3 forms of masonry construction present in New Zealand are Unreinforced Masonry Construction (UMC)-no longer used here; Fully Reinforced Masonry (FRM)- all our concrete masonry design here, and Confined Masonry Construction (CMC)- the masonry elements are confined within.

Each standard block has 60% porosity. In addition to the standard blocks, the system has blocks which contain a 175 diameter mm void into which reinforcing bars are placed and solid poured to form reinforced concrete columns, with an effective cross-sectional dimension of 150x150mm to link with top & bottom reinforced concrete ring beams. These columns are positioned either side of openings exceeding 1.5 m2 in area, at all corners and structural wall junctions at 5.0m centres max. These are used throughout the building.

Average compressive strength = 9.0 N/mm2. Base value (unfactored or allowable compressive strength) = 1.5 N/mm2. Density = 6.8 kN/m2 (including voids).

As with all masonry design the structure relies heavily on diaphragm restraint at ceiling level being achieved with either construction play in the lower seismic zones or pre-stressed concrete in the higher seismic areas.

EBOSS Article - Earthquake-Resistant Construction with Porotherm Clay Block - Stellaria NZ Wienerberger Porotherm Clay Block Construction -Shaking_table

Fired clay brick masonry constructions are one of the oldest construction methods dating back to 4000BC. Most historical buildings still in existence have been constructed with clay bricks with the timeless benefits of clay being a natural & healthy building material, having long term durability and in today’s construction environment lasting capital value as well as excellent thermal properties and excellent mechanical performance.

Wienerberger, who are the manufacturer of Porotherm clay blocks, was founded in 1819 and is today the largest producer of clay products and also the leading global innovator in the development of structural clay components with their ‘fabric first’ approach being a trendsetting world leader in the building industry.

Fired clay blocks are optimised according to technical and economic requirements necessary to meet mechanical stability, thermal & sound insulation, fire resistance as well as construction costs. Modern construction standards are increasingly challenging especially in all global higher seismic zones.

In order to meet higher seismic requirements a new block was developed by Wienerberger to be used in very high seismic zones in Europe. The patented Porotherm-S block. This block uses extra conventional mortar distributed through internal pockets within the blocks thereby minimising thermal leakage through the joints. It is well understood that mortar joints become cold bridges, decreasing the thermal properties so Wienerberger developed a particular clay mixture to retain thermal conductivity as well as maintaining high mechanical strength. Cyclic shear tests have been performed on this Unreinforced Masonry System (URM– no steel reinforcing) where vertical compression was kept at a level of 0.60 N/mm2 in order to simulate the load of three upper storeys. The results from these tests showed that the structure still hadn’t reached its Ultimate Limit State (ULS) at a Peak Ground Acceleration (PGA) of .75g.  By comparison New Zealand’s PGA zones range from 0.13g in the upper North Island to Wellington at .45g and our severest at Westport being 0.50g. You can appreciate then the performance level in New Zealand of Porotherm clay block homes where we do use a reinforced Confined Masonry Construction system.

More Information – Wienerberger, SERIES (Seismic Engeneering Research Infrastructure for European Synergies)

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