International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-10 of 26 Abstracts search results

Document: 

SP55-25

Date: 

August 1, 1978

Author(s):

Hubert Rusch

Publication:

Special Publication

Volume:

55

Abstract:

The purpose of Closing Remarks is usually to integrate the concepts contained in contributions to a symposium volume with the intention of showing new directions for future work, I hope you will forgive me if I deviate from this pattern, I feel that this symposium volume in memory of our common friend Douglas McHenry should not be concluded without our having paid tribute to the example that he offered us as a researcher, It first occurred to me how advanced McHenry's fundamental approach to research was when in 1965 I attended a lecture by the British biologist and Nobel Prize winner Medawar who analyzed the implications of the rapidly burgeoning quantity of scientific data. He prophesied that researchers, even in specialized fields, would be progressively snowed under by numerical data. The human brain is incapable of storing accessibly such a host of records and thus cannot synthesize the data into new ideas, Medawar therefore emphasized the necessity of replacing the many keys opening doors to single rooms with one master key giving direct access to a whole building. He warned against relying on computer systems for extracting meaning from masses of data. Computers cannot replace insight and creativity. The intention of referring to Medawar's statement is to show that McHenry's work as a researcher was inspired to a large extent by a similar spirit, His famous paper "A New Aspect of Creep in Concrete and its Application to Design" (1), published in 1943, typifies his innovative approach. It is a paper full of new ideas, anticipating future developments, but is at the same time an effort to find the master key the designer desperately needed,

10.14359/6631


Document: 

SP55-24

Date: 

August 1, 1978

Author(s):

C.K. Chen, R.M. Czarnecki, and R.E. Scholl

Publication:

Special Publication

Volume:

55

Abstract:

Results of a high-amplitude, destructive-level vibration test of a full-scale, 4-story reinforced concrete bare-frame structure indicated that the dynamic response characteristics remained rela-tively constant at motion amplitudes less than the calculated elastic limit (but above the design capacity of the structure). However, as this limit was exceeded, the structure exhibited nonlinear response behavior that was accompanied by significant variations in the dynamic characteristics, causing major structural damage. Empirical relationships relating inelastic response properties to elastic response values and ductility were developed. Although these relationships were derived from data of this test structure, they may be used to predict the approximate range of inelastic response of reinforced concrete structures from known elastic response properties and expected ductility factors. This paper also compares the structure's response properties resulting from lower-amplitude vibration tests conducted before and after the high-amplitude destructive test (i.e., on the undamaged and damaged structure). The response of the damaged structure to forced vibration appears to be consistent with the response of the undamaged structure except that the damaged structure exhibited larger periods, higher damping ratios, and some deflected shape discontinuities.

10.14359/6630


Document: 

SP55-23

Date: 

August 1, 1978

Author(s):

Sigmund A. Freeman

Publication:

Special Publication

Volume:

55

Abstract:

A procedure for estimating the inelastic respond\se of reinforced concrete structures to ser\severe ground motion is described. This procedure combines analytical structural engineei\ring methods with interpreitve analyses of response spectra and can be used by practicing engineers without complex computer analysis. The solution results in estimated values for peak structural response, peak ductility demands, equivalent responese periods of vibration, equivalent percentages of creitical damping, and reserve capasities. Examples of the procedure are presented, and their results are compared with data obtained from recorded motion of actual reinforced concrete structures.

10.14359/6629


Document: 

SP55-22

Date: 

August 1, 1978

Author(s):

Basile G. Rabbat and Michael P. Collins

Publication:

Special Publication

Volume:

55

Abstract:

The paper presents a model capable of predicting the post-cracking response of reinforced and prestressed concrete members subjected to complex loading. The angles of inclination of the compression diagonals in the walls of the truss model are determined from strain compatibility conditions. These compatibility conditions in conjunction with the equilibrium conditions for the truss and the load-deformation relationships for the members of the truss enable the full response of the model to be determined; i.e. the strain in the longitudinal and web reinforcements as well as the various eformations of the beams at all load levels can be predicted. Experimental results are used to confirm the truss model's predictions. It is shown how the truss model could be used in the design office.

10.14359/6628


Document: 

SP55-21

Date: 

August 1, 1978

Author(s):

J. Misic and J. Warwaruk

Publication:

Special Publication

Volume:

55

Abstract:

This paper presents details of an analysis for strength at failure of prestressed beams subjected to a complex system of applied loads consisting of combined torsion, shear and bending. It is based on a modified skew bending approach incorporating the use of strain compatibility over the beam cross-section to permit recognition of a "non-flat" yield region typical for cold drawn reinforcement. A significant feature of this analysis is the use of a biaxial strain criterion to recognize that the magnitude of the limiting strain in the compressed concrete at failure varies with different combinations of torsion, shear and bending. Other contributors working on this problem have used either a constant limiting concrete strain of magnitude 0.003 as for pure flexure, or some constant fraction of this amount throughout all possible load combinations involving torsion, shear and bending. Incorp-orated also in the determination of the ultimate strength is the ' recognition of the presence of shear stresses on the uncracked failure surface. Results of tests made on eighty four beams were used to verify this analysis. An excellent and consistent correlation was obtained between theoretical and test values for bending moments and resisting torques.

10.14359/6627


Document: 

SP55-20

Date: 

August 1, 1978

Author(s):

M. Betzle

Publication:

Special Publication

Volume:

55

Abstract:

Lapped splices play an important role in the con-struction of reinforced concrete structures. The tensile force at a reinforced bar end is transferred over the concrete to the beginning of the next bar by means of tbe bond action alone. Investigations on the capacity of lapped splices were carried out at the Institute for Structural Engineering, University of Technology, Munich. This research was initiated by Professor Kupfer. The purpose of these tests was to gain more knowledge regarding the stress in the surrounding concrete and to ascertain the force distribution along the spliced bars. The first part of the research program comprised of slab tests with full splicing of reinforced bars with large diame- ters. For the judgement of the capacity of a reinforcing bar the most important criterion is the bond behaviour of the concrete and steel along the lapping length. By means of a new method specially developed for this research it was possible to measure the slip of the spliced bars in comparison to the concrete within short distances along the bar with scarcely any bond disturbance. In connection with the steel strain, measured by bonded wire strain gauges, it was possible to ascertain the bond strain-slip relations (C-A) for different sections of the lapping length. Parallel to these tests, investigations on photoelastic models were carried out. These tests in conjunction with a special technique allowed the spacial course of stress in the vicinity of the reinforced bar to be studied. With the aid of the bond laws derived from reinforced concrete tests and the knowledge gained from the photoelastic tests the splices were calculated on the basis of the finite element method and compared with the results obtained from tests.

10.14359/6626


Document: 

SP55-19

Date: 

August 1, 1978

Author(s):

M. Ladner

Publication:

Special Publication

Volume:

55

Abstract:

Field measurements on two existing reinforced concrete slabs had to show that the chosen strengthening methods were successful. This was done by determining the bending stiffnesses of the two slabs before and after strengthening. The strengthening methods and the measuring equipment are described. The results showed that the sub-sequent strengthening provided an increase of the bending stiffnesses. It was also found that to achieve good quantitatif results a load test is required, whereas the actual floor loading produces only qualitatif results.

10.14359/6625


Document: 

SP55-18

Date: 

August 1, 1978

Author(s):

Gerd Thielen

Publication:

Special Publication

Volume:

55

Abstract:

The random behavior of reinforced concrete elements at de-formational limit states and at the ultimate limit state is analyzed by a second moment approximation. The deterministic and stochastic parameters involved, their functional and stochastic dependences, and their experimentally based statistics are discussed. The resulting variances of ultimate carrying capacity and ductility and of crack development are shown. It should be noted that ultimate ductility has an especially strong statistical variation independent of the amount of compressive reinforcement. A two-span beam is analytically modeled to elaborate first order approximations of the means and variances of simultaneously acting live loads and temperature effects which cause different limit states. Imposed deformations do not greatly influence ultimate load-carrying capacity provided that there is sufficient ultimate ductility. However, load-carrying capacity with respect to a limit state of allowable crack width is substan-tially reduced by simultaneously acting imposed deformations.

10.14359/6624


Document: 

SP55-17

Date: 

August 1, 1978

Author(s):

Y. Anderberg

Publication:

Special Publication

Volume:

55

Abstract:

Analytical predictions of thermal and mechanical behaviour of reinforced concrete structures exposed to differentiated complete fire processes including the cooling phase are presented and verified by tests. The modelling of the fire response comprises a heat flow ana-lysis in the first step and a structural analysis in the second step, based on two separate computer programs. The evaluated structural fire response is compared with the measured behaviour in a great number of experimental tests in which, the fire process and the external load level are widely varied. The experimental investigation refers to a well-defined hyperstatic structure, viz. a reinforced concrete plate strip fire-exposed on one side and completely fixed against rotation at both ends while axial movement is free to develop. The outline of the project is built on the philosophy of a functionally based, dif-ferentiated design procedure for fire exposed, load-carrying and separating structures. Such a design procedure refers to performance criteria and postulates that the real physical processes with res-pect to fire exposure, heat transfer and structural behaviour are predicted as far as possible.

10.14359/6623


Document: 

SP55-16

Date: 

August 1, 1978

Author(s):

Y. Anderberg, S.E. Magnusson, 0. Pettersson, S. Thelanders-son, and U. Wickstrom

Publication:

Special Publication

Volume:

55

Abstract:

The principles are presented for the main types of the dif- . ferentiated, structural fire engineering design systems, in practice at present or anticipated to be applied in the future. Such design systems are generally based on real fire exposure characteristics, given by the gastemperature-time curves of the complete fire process and specified in detail with respect to the influence of fire load and the geometri-cal, ventilation and thermal properties of the fire compartment. The design procedure can be in its entirety analytical or combined analyti-cal and experimental. In the latter case, real fire exposure conditions can be transferred to the heating conditions according to the standard fire resistance test via the concept equivalent time of fire duration. Starting from the present state of knowledge, the possibilities are discussed for a practical application of a complete analytical, diffe-rentiated design in regard to fire exposed, reinforced and prestressed concrete structures. Finally, the various sources and kinds of uncer-tainty in the differentiated design procedure are briefly dealt with within the framework of the structural fire safety problem.

10.14359/6622


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