Design of Concrete Structures

Engineering 5706

Laboratory Instructions for Reinforced Concrete Beams

Laboratory Work

In general, the laboratory report should be complete, concise, clear and presentable. The following items should form the base of the report:

  1. Introduction and Objectives (Scope and purpose): State precisely what you are studying and what you plan to observe.
  2. Experimental Set-up: Describe the physical set-up with the help of figures.
  3. Instrumentation: indicate the types and locations.
  4. Test results: Include original data either in the body of report or in an appendix. Do not re-copy it to make it look neater.
  5. Discussion: Discuss the results and compare with theory and with the results of tests by other tests. Give a detailed account of the accuracy of results.
  6. Conclusions.

Justification for important decisions made along the way (main dimensions, materials, support conditions, etc.) should be discussed briefly.

Problems encountered in conducting the experiment may also be discussed, along with any recommendations on how the test set-up and instrumentation might be improved.

A single report on each experiment is to be submitted by each group. In addition to technical content, the organisation, clarity and neatness will be considered in assessing the report. In other words, the report should look as professional as possible.

 

OBJECTIVES

Among other things, the objectives include a study of the strength and behaviour of reinforced concrete beams. A beam will be tested under a concentrated load until failure. The cracking pattern and the failure characteristics will be observed. Finally, the nominal ultimate capacity of the beam will be recorded and compared to those obtained from theoretical calculations.

REFERENCES

CPCA Handbook, Class Notes, Text book by Pillai and Kirk. 

EQUIPMENT

  1. Loading frame.
  2. A hydraulic actuator with a maximum capacity of 670 kN, and a full stroke of 150 mm.
  3. A closed loop MTS testing machine operating in the displacement and/or load control.
  4. Concrete and steel strain gauges (optional).
  5. Data Acquisition and Control System (optional).

 

CASTING PROCEDURE

The following procedure will be undertaken by each individual group:

  1. Analyse the given reinforced beam based on the information provided and as discussed in the class.
  2. Assemble the form-work for the beam and the reinforcement.
  3. Cast the beam. Casting date will be announced in the class.
  4. Testing date will be around four weeks after the casting.
  5. Two control cylinders (150x300 mm) will be cast for each group and or mix.

TESTING PROCEDURE

The following procedure will be undertaken by each individual group:

  1. Control cylinders will be tested and the compressive strength, fc, will be obtained.
  2. Depending upon availability of facilities, a tensile test will be done on the reinforcement used to determine the ultimate tensile strength.
  3. On the day of the test, the beam will be stripped of the covers and moved to the structures lab. The general procedure of the experiment will be as follows:

  1. A concentrated load will be applied to the beam at mid-span with a hydraulic actuator.
  2. The load will be increased in approximately 2 kN increments until the beam fails.
  3. During the test, and at the end of each load step, the beam will be inspected, the deflection will be recorded and the crack patterns will be observed and marked until failure.

 

REPORT

Among other things, the report, by each individual group, shall consist of the following:

  1. Details of the beam with sketches.
  2. Complete design of beam(s) before casting and complete analysis for the beam(s) after testing.
  3. Procedure followed on the day of pour.
  4. Results of cylinder test and reinforcement test (if carried out).
  5. Procedures followed on the day of testing.
  6. Type of failure(s) that occurred.
  7. A schematic of the crack development in the beam (and a photograph if possible).
  8. Comparison of theoretical versus recorded data.
  9. Comparison with the data of other group(s).
  10. Comments and observations.

 

GIVEN DATA

Basic Shapes of Beams:

Loading arrangement:

The reinforced concrete beam is to be deigned using to the following data:

Dimensions: Each group will be given a beam dimension. The form-work for the beam is available at the concrete lab. The beam has either a Rectangular section or a T-section.

Reinforcement: Grade 400 steel. Four sizes are used; #10, #15, #20 and #25 metric size. The top bars shall be #15 size.

Concrete: the concrete will be delivered by a truck on the day of pouring. The nominal compressive strength of the concrete, f c, is 35 MPa. Actual strength will be as per cylinder tests.

Beam: The beam will be cast for a length of 8 ft. The beam is simply supported with a span of 7.5 ft. The beam web is either 6" or 8". The overall depth is 12". For T-beams, the flange thickness will be 3" and flange projection from the face of web will be 4". The beam is in an interior and non-corrosive environment. Nevertheless, the concrete cover should be measured from the actual reinforcement cage and form-work of the beam before casting the concrete. Stirrups will be #10 size metric bars. Recommended spacing of stirrups is 100 mm (may be varied if necessary).

RESULTS REQUIRED

Complete analysis of the beam should be carried out. In doing the calculations, assume that the laboratory test load is the factored load (do not apply load factors). If using the actual measured material strengths, do not use the resistance factors. The following should be calculated:

  1. The ratio of the actual reinforcement to that of the balanced reinforcement,
    ractual/rbal, (you have to calculate the balanced reinforcement ratio, rbal, of the beam).
  2. The cracking moment of the beam.
  3. The ultimate moment of the beam.

  1. The cracking load and maximum load at the centre of the beam. Draw the bending moment and the shearing force diagrams.
  2. P-D calculations.

DEFORMATION CHARACTERISTICS

Deflections

The deflection at centre of the beam is measured using the internal LVDT of the hydraulic actuator. Additional dial gauges may be used as well.

Steel Strains

The steel strains can be measured in the centre of the span by means of electrical strain gauges. The steel electrical strain gauges are 10 mm long, 120 W resistance and a gauge factor of 2.04 .5 %. For protection against any possible water damage during casting, the strain gauges are coated with a sealant.

Concrete Strains

The concrete strains can be measured in the centre of the span by means of electrical strain gauges. The concrete electrical strain gauges are 50 mm long, 120 W resistance and a gauge factor of 2.07 .5 %. The strain gauges are glued on the concrete surface on a very thin layer of Epoxy bonding agent used to obtain an even surface.

SUBMISSION

Deadline line for submittal of the lab report is one week after the test.

EVALUATION

The evaluation of the lab work and report will be based on the following evaluation criteria

1.

Appearance of form-work and reinforcement cage

5 %

2.

Concrete finish

5 %

3.

Prediction of ultimate load

10 %

4.

Complete analysis of the beam

35 %

5.

Description and analysis of the results

35 %

6.

Completeness and accuracy of final report

10 %

7.

Negative marks will be applied for not meeting deadlines and improper work.

 

Depending upon the performance, a short interview may be conducted to evaluate individual students in each group.