Lect2 1151 grillage analysis PDF

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Download Lect2 1151 grillage analysis PDF

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Grillage Analysis of Girder Bridges

Course Coordinator: Dr Rebecca Gravina

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

The challenge • In designing a girder bridge, the design actions under factored design loads are needed for the girders as well as the deck slab, which include – Bending moment – Shear Force – Torsional moment – Deflections • In a previous version of the Bridge code, design loads were calculated using distribution factors • Current version of the Austroads code AS5100 doesn’t provide distribution factors, hence • A more sophisticated analysis method is needed – Grillage analysis – Finite element Analysis

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Design Codes • AS3600 concrete structures • AS5100.1 Bridge design – part 1 Scope and general principles • AS5100.2 Bridge design – part 2 Design Loads • AS5100.1 Bridge design – part 5 Concrete

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Grillage Analysis •Structure is idealised as a number of longitudinal and transverse beam elements in a single horizontal plane, rigidly interconnected at ends •Transverse beams may be orthogonal or skewed with respect to longitudinal beams to analyse irregular decks •In a simple grillage analysis, each beam is given a flexural stiffness in the vertical plane and a torsional stiffness •A software program is used to conduct a matrix stiffness analysis to determine the design actions

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Spacegass has the facility to perform a grillage analysis

copyright © SPACE GASS

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Typical Grillage Model

copyright © SPACE GASS RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

More on Grillage Analysis

• Main Longitudinal beams are assigned the flexural properties of the full section of each girder including the deck slab • Loads are only applied at the nodes and also as concentrated loads along members • The analysis does not take into account the shear lag nor the distortion of the section • Deck slab is modeled as transverse elements of rectangular cross-section • Localised effects will need to be considered separately – eg. Wheel load being applied on the slab in between two longitudinal beams

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Longitudinal element

Australian Standard®, Bridge Design Part 5: Concrete Design RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Most common prestressed concrete sections Australian Standard®, Bridge Design Part 5: Concrete Design

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 5: Concrete Design

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Modeling of Box Girder Bridges may include an additional dummy element

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Austroads Bridge Design Code – AS5100 2004 Part 2 Design Loads • Dead Loads • Road Traffic • Collision Loads • Water Flow • Wind Loads • Thermal Effects • Etc..

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Load Combinations

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Load Combinations Contd..

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Superimposed dead load • Dead loads likely to change during the lifetime of the structure

– Surfacing material, tram tracks, pipes, conduits, cables

Australian Standard®, Bridge Design Part 2: Design Loads RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Traffic Loads

Australian Standard®, Bridge Design Part 2: Design Loads RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Australian Standard®, Bridge Design Part 2: Design Loads

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Major Design Project

• Design of the prestressed concrete girders for a bridge of given specification • You may select an I section from the standard sections of the code • Model the bridge deck using a grillage • Apply selected design loads and analyse for combined effect – both ultimate limit state and serviceability limit state • Calculate the prestress force and the tendon configuration for the girders • Perform design checks for bending strength, shear, deflections, torsion

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Spacegass grillage analysis - Inputs

• Input section details of RC bridge deck and PC bridge girder using section property input in Spacegass – for deck use shape builder function for rectangular element with section details – 180mm thick x 1250mm wide (use 1.25m spacing to match traffic axle wheel spacing) – For PC bridge girder use shape builder function to build I-section

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Spacegass grillage analysis - Inputs

• Load case inputs – Load case 1: self weight of girder and bridge deck (spacegass calculates provided you have specified section size and material type) – Load case 2: superimposed dead load – Load case 3: S1600 stationary Traffic load – lane 1 – Load case 4: S1600 stationary Traffic load – lane 2 – Load case 5: M1600 moving Traffic load – lane 1 – Load case 6: M1600 moving Traffic load – lane 2

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

Spacegass grillage analysis - Inputs • Combination Load case inputs – Load case 10: Serviceability = total Dead load + S1600 lane 1 +0.8(S1600 lane 2) – Load case 11 : Ultimate 1.2x(total Dead load) + 1.8x(S1600 lane 1 +0.8(S1600 lane 2) ) – Load case 12: Serviceability = total Dead load + M1600 lane 1 +0.8(M1600 lane 2) – Load case 13: Ultimate 1.2x(total Dead load) + 1.8 (M1600 lane 1 +0.8(S1600 lane 2))

(note apply 0.8 accompanying load factor only to lane 2 loading

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina

RMIT University©

Lecture Notes prepared by Dr Rebecca Gravina...