PSC T girders

4.7.5.1 T girder dimensions

• T girders shall have diaphragms and the maximum void length between diaphrams shall be 5.0 m.

• T girder dimensions and void arrangements shall be in accordance with Figure 4.7.5.1 and Table 4.7.5.1 respectively.

Chapter 4: Bridge component design requirements

Table 4.7.5.1 – Void arrangement of T girders (Indicative only)

Nominal Length (m)

T girder void arrangement

Nominal Length of End Blocks (mm) Nominal Actual Girder Length (mm) No. of 5 m Voids No. of 2.5 m Voids No. of Internal Diaphragms (150 mm) 20 3 0 2 2325 19950 21 3 0 2 2825 20950 22 3 1 3 2000 21950 23 3 1 3 2500 22950 24A 3 1 3 3000 23950 24B 4 0 3 1750 23950 25 4 0 3 2250 24950 26 4 0 3 2750 25950 27 4 1 4 1925 26950 28 4 1 4 2425 27950 29 4 1 4 2925 28950 30 5 0 4 2175 29950 31 5 0 4 2675 30950 32A 5 0 4 3175 31950 32B 5 1 5 1850 31950 33 5 1 5 2350 32950 34 5 1 5 2850 33950 35 6 0 5 2100 34950 36 6 0 5 2600 35950 4.7.5.2 End diaphragms

a) T girder superstructures shall be designed with a diaphragm at each pier and abutment to ensure uniform distribution of loads during jacking to replace bearings.

b) T girder diaphragms or cross girders shall be poured separately from the reinforced concrete deck because the diaphragms provide stability during pouring of the concrete deck. The diaphragms shall be poured and the concrete cured before the deck is poured. This shall be detailed on the drawings.

c) Because the diaphragms provide stability during pouring of the concrete deck, they shall be poured and the concrete cured before the deck is poured.

4.7.5.3 Maximum skew angle

a) Concrete trough and "Super Tee" girders shall not be cast with skews exceeding 45 degrees. This requirement relates to practicality of casting yards.

Chapter 4: Bridge component design requirements

b) Note: When the skew of the superstructure exceeds 45 degrees, this can be achieved by installing the T girders on the actual skew, but ends of the precast girders shall be detailed at 45 degrees (acute angle of the girder ends).

c) The ligatures shall be fanned at the ends and transition to be perpendicular to the girder longitudinal axis. Refer Transport and Main Roads Drafting and Design Presentation

Standards Manual, Chapter 14 for typical reinforcement arrangement at the skew ends of the girders.

4.7.5.4 Half-joints not permitted

Stepped or half-joints shall not be used in bridge girders.

4.7.5.5 Sacrificial formwork for T girders

The sacrificial formwork for the insitu reinforced concrete deck over T girders and between the flanges of T girders shall comply with the following requirements:

4.7.5.5.1 Design loads

a) The design loads to be applied to the formwork are:

• self weight, and

• construction loads.

b) The limit state design requirement for strength, stability and stiffness (deflection) shall be in accordance with AS 3610 Table 4.5.1

4.7.5.5.2 Construction loads

The construction loads on the formwork shall be considered in two stages. Stage 1 is prior to the placement of the concrete deck and Stage 2 is during the placement of the concrete deck.

a) Stage 1 loads:

• Concentrated load that shall be in accordance with AS 3610 – 1995 Formwork for Concrete. This load shall be multiplied by 1.25, which is the recommended impact factor.

• This load can be due to construction materials, such as bundles of reinforcing steel and construction foot traffic.

b) Stage 2 loads:

• Wet concrete, and

• Concentrated load which shall be in accordance with AS 3610 – 1995 Formwork for Concrete.

Wet concrete and concentrated load shall be multiplied by 1.25 (dynamic impact factor). These loads take into account the placement of the concrete. They also take into account the loads generated by construction foot traffic and the equipment used in the placement of the concrete.

4.7.5.5.3 Edge support of formwork

The minimum edge support dimension shall be 25 mm continuous along four sides of the formwork. The strong direction of the formwork shall span across the T girders.

Chapter 4: Bridge component design requirements

4.7.5.5.4 Acceptable deflection

The deflection shall be determined in conjunction with the combinations specified in AS 3610 “Formwork for Concrete” Table 4.5.1 and the addition of the concentrated load. The maximum allowable deflection for all stages of construction shall be span/360 for all products.

4.7.5.5.5 In-service stress

The maximum ultimate limit state stresses during all stages of construction shall be less than the specified flexural strength of the material.

4.7.5.5.6 In-fill sheets

a) Fibre Cement (FC) In-fill Sheets

Fibre cement sheet is an accepted material for in-fills to T girders. The design criteria for the FC sheet shall satisfy the following:

• The deflection shall be in accordance with the acceptable deflection criteria, and

• The ultimate design stresses shall not exceed the flexural strength of the panels. b) Material Not Permitted as In-fill Sheets

The following materials are not permitted as in-fill sheets in T girders:

i. Plywood and wood-based panel products because moisture ingress degrades the material, which may then block drainage of the cells in the girder.

ii. Cold-formed steel sheet sections (for example, Bondek or similar) are not permitted due to deformation of profile during loading.

c) Alternative Products

i. Any product except those listed under (b) above as In-fill Sheets may be considered an alternative product.

ii. The product shall satisfy the following:

• Resist the design loads

• Be durable for 100 years

• Satisfy the deflection criteria outlined above, and

• The cross-sectional shape shall not change when the formwork is loaded. Testing may be required to verify the section does not change shape.

iii. The product shall be selected by the Designer, and detailed clearly on the deck drawings.

4.7.5.6 Transfer strength of PSC T girders

PSC T Girders shall be designed with concrete strength at transfer greater than or equal to 35 MPa, and less than or equal to 40 MPa.

4.7.5.7 Debonding of strands

Chapter 4: Bridge component design requirements

4.7.5.8 Maximum tendon force at transfer

The maximum pretension force in a tendon at transfer shall not be greater than 75% of the minimum breaking load of tendon.

4.7.5.9 Lifting of PSC T girders

Lifting points for PSC T girders shall be designed and RPEQ certified in accordance MRTS73 by the designer.