Detailing Aspects of the Reinforcement in Reinforced ... · PDF fileiii Detailing Aspects of the Reinforcement in Reinforced Concrete Structures Retaining wall (case study) By Timothy

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Detailing Aspects of the Reinforcement in

Reinforced Concrete Structures

Retaining wall (case study)

By

Timothy Ovainete Saiki

in partial fulfilment of the requirements for the degree of

Master of Science in Civil Engineering

at the Delft University of Technology, to be defended publicly on Thursday July 28, 2016 at 10:00 AM.

Supervisor: Prof. dr. ir. D.A. Hordijk Thesis committee: Dr. ir. drs. C.R. Braam, TU Delft

Dr. ir. P.C.J. Hoogenboom, TU Delft

An electronic version of this thesis is available at http://repository.tudelft.nl/.

http://repository.tudelft.nl/

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Acknowledgement

I would like to express my gratitude to Prof.dr.ir. D.A. Hordijk for his invaluable contribution to this MSc

thesis. The guidance he provided and the quality he demanded at all times were vital to this achievement. I

would also like to express my gratitude to my direct supervisor, Dr.ir.drs. C.R. Braam for his patience, the

knowledge he shared and other contributions made during the course of this MSc thesis. I also like to

express deep gratitude to Dr. Ir. P.C.J. Hoogenboom for the guidance he provided and the support he

provided towards the realization of this thesis.

Finally I would like to then my wife (Vovo) and daughters (Ofushi & Enworo) for the unconditional support

they gave me over the past two year. I look forward to returning to you soon, never to leave again. Thank

you a million times!!!

Timothy O. Saiki

Delft, July 2016

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Summary This thesis studies the impact of reinforcement detailing on the behaviour of a reinforced concrete structure.

Using a retaining wall as a case-study, the performance of two commonly used alternative reinforcement

layouts (of which one is wrong) are studied and compared. Reinforcement Layout 1 had the main

reinforcement (from the wall) bent towards the heel in the base slab. For Reinforcement Layout 2, the

reinforcement was bent towards the toe. This study focused on the reinforcement details used in the D-

region, and on how it impacts the capacity, joint efficiency and failure mode of the structure.

First, a literature review is carried out which focused on the behaviour of corner joints from experimental

works available in literature. Next, a strut and tie model of the D-region is made. From the strut and tie

model, the opening moments acting on the structure subjects the re-entrant corner region to a concentration

of tensile stresses, while a compressive stress field acts concurrently with transverse tension within the core

of the joint. The internal forces within the D-region are evaluated, and the required steel areas computed.

Afterwards, ATENA FEM software is used to model the structure, and to study the impact of the alternative

reinforcement layouts on the capacity and behavior of the structure. Some aspects of the structural behavior

studied include the stress and strain distribution in the concrete, crack width, crack pattern, steel stress and

strain distribution etc.

The results obtained from the FEM analysis was sensitive to bond model defined in the material model.

When perfect-bond was assumed in the FEM analysis, Reinforcement Layout 1 attained a joint efficiency

of 72.4%, while Reinforcement Layout 2 achieved 88% joint efficiency. In his experimental works on

similar details, Nilsson (1973) had obtained a joint efficiency of 60% for Reinforcement Layout 1, a range

between 82% to 102% for Reinforcement Layout 2. The disparity between FEM result and experimental

result for Reinforcement Layout 1 occurred because perfect-bond was assumed in the FEM model. With

cracking playing prominent role in this structure, perfect bond assumption is not valid, and some slip is

inevitable. To verify, a bond-slip relation is used to model the structure, resulting in 62% joint efficiency

for Reinforcement Layout 1, and 82% joint efficiency for Reinforcement Layout 2. These values obtained

with bond-slip model are much closer to experimental values than those obtained with perfect bond.

The reinforcement layout used also had significant impact on the joint behavior. In Reinforcement Layout

1, the reinforcement (tie) from the wall was not properly anchored in the nodal region in the slab. The

compressive stress field (i.e. inclined strut) was observed to flow past the bent part of the reinforcement

without much interaction. The force transfer between the inclined strut and the tie was not effective. Also,

wide cracks occurred along the inclined strut from the action of transverse tension (caused by the opening

moment). These cracks which further weakened the strut. This detail had a diagonal tension cracking failure

mode. For Reinforcement Layout 2, a clearly defined nodal region exists. A CTT node formed allowed for

effective force transfer (at the node) between the concrete and steel. Furthermore, the bent part of the

reinforcement crossed the path of the inclined strut, and helped to control crack width. The reinforcement

also provided confinement to the inclined strut which further increased its strength. This detail prevented

diagonal tension cracking failure, hence the higher capacity it achieved. Failure was by crushing of concrete

along the joint slab interface, after formation of a wide vertical crack extending from the re-entrant corner

downwards into the slab. Adding a diagonal bar, placed 45 around the re-entrant corner, helped to control

this re-entrant corner crack, thus ensuring that over 100% joint efficiency is achieved. In conclusion,

Reinforcement Layout 1 is a poor detail. Though common in practice, the nodal is not properly formed in

this detail. This makes force transfer between concrete and steel sub-optimal. The detail should be avoided.

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Contents

Acknowledgement ........................................................................................................................................ v

Summary ...................................................................................................................................................... vi

Contents ..................................................................................................................................................... viii

1 Introduction .......................................................................................................................................... 1

1.1 Background ................................................................................................................................... 1

1.2 Aim of the study ............................................................................................................................ 1

1.3 Method of study ........................................................................................................................... 2

1.4 Outline of the report ..................................................................................................................... 2

2 Detailing of structures and Strut and Tie Model................................................................................... 4

2.1 Extent and behaviour of D-regions ............................................................................................... 4

2.2 Strut and tie model ....................................................................................................................... 5

2.3 Developing the strut and tie model .............................................................................................. 7

2.4 Dimensioning of strut and tie ....................................................................................................... 9

2.4.1 Struts ................................................................................................................................... 10

2.4.2 Ties ...................................................................................................................................... 12

2.4.3 Nodes .................................................................................................................................. 12

2.4.4 Dimensioning and design of struts, ties and nodes ............................................................ 15

2.5 Applications of strut and tie model ............................................................................................ 18

2.5.1 Corbels ................................................................................................................................ 18

2.5.2 Corner Joints ....................................................................................................................... 20

2.6 Detailing ...................................................................................................................................... 27

2.6.1 Some basic rules.................................................................................................................. 27

2.6.2 Bond and anchorage ........................................................................................................... 29

2.6.3 Splicing of bars .................................................................................................................... 31

3. Behaviour and detailing of corner joints .......