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Ponašanje čeličnih okvirnih građevina sa zidanim ispunom pri djelovanju potresa

This thesis presents difficulties related to the design and execution of steel frames with masonry infill.
These types of structures are relatively often and significant research on their behavior was conducted from
the second half of the past century. Despite numerous investigations related to the evaluation of behavior
that these structures exhibit under significant horizontal loads, because of their complexity there is still no
applicable method for their reliable assessment, as it is the case with simpler constructions.
Results of original experimental investigation of steel frames with masonry infill are presented and
discussed. This investigation included determination of mechanical characteristics of materials used in
such a composite system (masonry and steel), and obtained results were used for calibration of infilled
steel frame subjected to horizontal loads numerical models. Experimental research of steel frames with
masonry infill was carried out through three series that each had three samples which differed by different
types of masonry infill, and on a frame without infill in order to determine the contribution that infill has to
strength and stiffness of the composite system. First series samples enabled the investigation of steel
frames with hollow clay bricks as infill, second sample had lightweight autoclaved aerated concrete (AAC)
blocks as infill, and third had infill comprised of both hollow clay and AAC masonry elements. The principle
behind the idea of combining infill elements is that „softer“ components (AAC blocks), which link the steel
frame columns with hollow clay bricks, fail first during seismic loading, thus enabling independent
movement of the steel frame in order to utilize its ductility. This behavior is favorable during seismic loading
due to the fact that masonry infill provides initial positive contributions to the strength and stiffness of the
whole system, but after its failure significantly reduces residual ductility of the steel frame.
Presented system with combined masonry elements, of different mechanical properties, can significantly
improve the behavior of infilled frames under earthquake loading, and at the same time does not
significantly change the building technology, requires no special installation tools and no additional
resources. As such, its use can be a rational solution when it comes to seismic isolation of masonry infill
from steel frames.
On the basis of experimental results it was possible to investigate the applicability of various numerical
models when it comes to prediction of such systems behavior. Test results were also used for the
calibration of numerical models that enabled implementation of an extensive parametric analysis with the
objective of determining the influence and importance that certain parameters have in such composite systems. Contribution of various masonry elements to the strength and stiffness of infilled steel frames
loaded horizontally was analyzed through a numerical example of a multistory, multi-bay construction.
Scientific contribution of this thesis is further clarification of behavior that steel frames with masonry infill
exhibit under horizontal loads, and a proposal of a simple construction method which enables the
prevention of adverse interaction between masonry infill and steel frame through damage control of specific
areas of the infill. Such a methodology could be applied in engineering practice for optimal design and
evaluation of behavior of steel frames with masonry infill in seismic and non-seismic areas.
Further scientific contribution is reflected through forming of an experimental database, which can be a valuable
source of information for additional research in this field.
An important part of this thesis is a critical review on the possibilities of different models for numerical analysis of
steel frames with masonry infill, as well as systematization of influence parameters conducted through extensive
parametric study.
Based on results acquired through this paper a new method of practical design of steel frames with masonry infill that
is consisted of different elements is presented.