Comments for Section 3 Flowchart   
Steps 1 to 4 (of 15)              

 

Step 1

 

Type, loading details

 

Step 1 involves the input of the relevant structural details and includes:

 

• Type of structure (e.g. bridge, beam… etc.) and design details (e.g. number of spans, length etc.)
• Material(s) of construction (e.g. concrete, masonry, timber, metallic (cast iron, wrought iron, steel))
• Structure configuration (e.g. over-bridge, rail or road crossing etc.)
• Structure history (e.g. previous strengthening etc.)
• Current capacity

 

 

Step 2

 

Design conditions

 

Step 2 involves the input of the relevant design conditions and includes:

 

• Loading type (e.g. dead, live, cyclic etc.) and magnitude
• Temperature
• Environmental conditions
• Abnormal loadings or other special conditions.

 

 

Step 3

 

Preliminary assessment

 

Step 3 represents a preliminary assessment as to whether the structure is suitable or not for strengthening. At this stage an additional survey and further testing of the structure may be required as there may not be sufficient information from Steps 1 and 2 for a decision to be taken. Before proceeding to the next step an initial decision that the structure is suitable for strengthening must be made.


Step 4

 

Material selection

 

Step 4 involves the material selection for the adhesive and composite reinforcement.

The input for this Step comes from the Classification Schemes for both adhesive and composite reinforcement, i.e. the designer selects the materials from the classification schemes using the terms of reference from the Client and design conditions. The selection involves:

 

• Fibre type
• Matrix (or resin) type
• Adhesive type
• Manufacturing method (including fibre orientation and lay-up, i.e. structure of the reinforcement)
• System properties.

 

The Designer should take note of the value of the material data quoted by the Material Supplier. Ideally the Material Supplier should quote characteristic values.

The characteristic value is defined as the mean value minus two standard deviations. In some instances the Material Supplier will quote a minimum value. However, it is recommended for consistency as discussion within the Classification Schemes that characteristic values are used throughout.

The choice of manufacturing method and structure of the reinforcement (the selection of the fibre orientation and lay-up sequence) are linked. This linkage limits the freedom of the designer in selecting the structure of the reinforcement. The choice of the manufacturing method is a critical selection in the design process. In selecting the manufacturing method the Designer should consider the potential issues of quality of manufacture, cost and whether to construct the reinforcement on- or off-site.

The material properties (characteristic values) required for flexural strengthening are discussed in the following sub-sections.

Substrate

The characteristic values for the substrate can be obtained from e.g. CIRIA C595 (2004) (steel substrate) or TR 55 (2004) (concrete substrate) or other relevant standards or guidelines.

The parameters required are modulus, thermal expansion coefficient and ultimate failure strain. In this general description of modulus, depending on the substrate, modulus should be interpreted as either linear or the relevant non-linear definition.

Adhesive

The design of the adhesive layer relates to the assessment of loads transferred between the substrate and the composite reinforcement through the layer. It is the adhesive layer system that is the critical unit, the combination of the adhesive, the substrate and the reinforcement.

The parameters (characteristic values) required are the peel and shear strength of the adhesive. The test methods are described in the Section on Classification Schemes.

Ideally these parameters should be long-term values. However, in most circumstances these long-term values are not readily available and short-term values multiplied by an appropriate partial factor are used.

Reinforcement

The characteristic values required are modulus, thermal expansion coefficient, moisture coefficient and ultimate failure strain. The test methods for determining these parameters are listed in the Section on Classification Schemes

Ideally these parameters should be long-term values. However, in most circumstances these values are not readily available and short-term values multiplied by an appropriate partial factor are used. Material Suppliers should be encouraged to generate long-term data for their products. The recommended test method for determining the long-term failure strain of a composite laminate is ASTM D 2990. Analysis of the data to derive the extrapolated long-term strain value is presented in ISO 14692. This would remove the need for both default material variability, , and reduction from short-term to long-term strength partial factor, .

The ultimate strain values required for design are long-term values, i.e. the ultimate strain for the reinforcement under constant load. Design practices used for composite vessels, tanks and over wrap repairs assume a conservative long-term ultimate strain of a composite laminate (independent of reinforcement fibre) of 0.25%. This default value of strain is recommended if no ultimate strain data is available, for example in the case of on-site lamination.