Deflection Estimation Model for Prestressed Concrete Slabs with Plastic Inserts Forming Voids.

Developed and patented more than 30 years ago, the system of slabs with plastic inserts has become very popular, and it is used all over the world today due to the significantly reduced cost of building construction. Experimental tests have shown that the behaviour of simple bending voided slab structures with plastic inserts during loading is very similar to that of solid slabs. However, their deflection and crack resistance are both slightly inferior to those of solid slabs. When using pretensioned reinforcement, the deflection and crack resistance of voided slabs exceed the above parameters for solid slabs. However, when using plastic inserts to form inner voids in slabs, their cross-section along the span becomes variable. In determining the stiffness of such slab, a problem arises in estimating the moment-of-inertia when the cross-section is variable. To estimate the influence of the voids formed by the plastic inserts on the deflection of prestressed concrete slabs, bending tests of two life-size reinforced concrete slabs were performed. The bending results obtained during the experiment were compared with the results obtained from the numerical model and analytical calculations.

Analysis of Physical and Mechanical Properties of the Mortar in the Historic Retaining Wall of the Gediminas Castle Hill (Vilnius, Lithuania).

This study analysed the results of the joint research into the building materials of the historic masonry of the retaining wall of the Gediminas Castle Hill dating back to the end of the 13th and beginning of the 14th centuries. Core samples for material testing were collected along the entire height of the retaining wall to assess its load bearing capacity. Boreholes were drilled 600⁻1000 mm from the exterior of the wall to determine the properties of the ceramic bricks and lime mortar that were not affected by external factors. The analysis of the microstructure and chemical composition, mechanical and physical properties of the ceramic bricks and lime mortar is presented. The high compressive strength (8.5 MPa) of the lime mortar was the result of using hydraulic lime and crumbs of ceramic bricks as mortar aggregate.

Investigation of the Behavior of Hardening Masonry Exposed to Variable Stresses.

This paper analyzes the behavior of masonry under variable loads during execution (construction stage). It specifies the creep coefficient for calcium silicate brick masonry, presenting the research data of masonry deformation under variable and constant long-term loads. The interaction of separate layers of composite material in masonry is introduced and the formulae for determining long-term deformations are offered. The research results of masonry’s compressive strength and deformation properties under variable and constant long-term loads are presented. These are then compared to calculated ones. According to the presented comparison, the calculated long-term deformations coincide quite well with those determined experimentally.