**Introduction** Gantry Girder

In a **manufacturing plant,** it is necessary to provide an overhead traveling crane to transport **heavy components** of **machines** from one place to another place. (Grasscrete)

The movement of the load is **three-dimensional**. The **crane **is needed to **lift heavy mass** vertically and horizontally, similarly, the crane with load is needed to move along the length of the **shed**. The **cranes **are either **hand-or-electrically operated**. The crane movement on the rails which are at its ends.

The **rails **are equipped on a girder is called a gantry girder. The **gantry girder** spans over **gantry columns.** If the capacity of the crane is moderate, the gantry girders rest on **brackets **attached to the roof column of the** industrial shed.**

**What Is Gantry Girder?**

**Gantry girders** or** crane girders **carry hand operated or **electrically operated **overhead cranes industrial buildings such as **factories, workshops, steelworks,** etc. to lift heavy materials, equipment, etc., and to take them from one location to the other, within the building.

The **gantry girders** are girders that support the loads that are conveyed through the **traveling wheels **of the crane. The** crane girder** spans from column to column, this generally does not possess any **lateral support** at the **intermediate points **excepting when a **walkway **is created at the **top of the girder**.

The **gantry girder **spans between the** brackets **connected to **columns**, which may either be of **steel or reinforced concrete.** Thus the span of the g**antry girder** is equal to the **center to center spacing **of columns. The **rails **are mounted on gantry girders.

The **crane girder **spans the bay of the shop. The **trolley or crab**, mounted on the **crane girder **can travel transversely along the crane girder. The **trolley **has** four wheels**. The crane girder has** two wheels** at each end and is capable of **moving longitudinally **on rails.

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**Loads On Gantry Girder **

- The gantry girders are unique in themselves
- First, it is
**unique from the usual beams**in buildings. It is laterally unsupported except at the columns. - Second, it is one of the very limited girders in the buildings that are
**subjected to impact**. - Third, it must be
**evaluated for unsymmetrical bending**because of lateral thrust from the starting and stopping of the crab. - Fourth, it is
**subjected to the longitudinal load**through the starting and the stopping of the crane bridge itself. - Fifth, these are
**often simply supported**. These are subjected to the forces as follows:- The reaction from the crane girder,
**working vertically downwards.** - Longitudinal thrust through the starting or the stopping of the crane,
**acting in the longitudinal direction.** - The lateral thrust, due to the starting or the stopping of the
**crab acting horizontally**, usual to the gantry girder.

- The reaction from the crane girder,

## Types of Gantry Cranes

The following are **gantry cranes types** used in construction,

- Full Gantry Crane Systems
- Semi-Gantry Crane Systems
- Portable Gantry Crane Systems
- Adjustable Gantry Cranes

**Types Of Load Acting On Gantry Girder**

Gantry girder, having no lateral support in its length (laterally supported) has to **resist the following loads**,

- Vertical Loads From Crane
- Impact Load From Crane
- Longitudinal Horizontal Force (Drag force)
- Lateral Load (Surge Load)

### 1. **Vertical Loads From Crane **

A **vertical load** working over the gantry girder is the outcome from the crane girder and includes the **self-weight of the crane, self-weight of the crab, **and **the crane capacity **(the ultimate load that can be hoisted).

To compute the reaction the **maximum wheel load** is calculated. It happens when the **crab **is nearest to the **gantry girder.** In addition, to the reaction from a crane girder, the **self-weight of the rail** should similarly be evaluated.

### 2. **Impact Load From Crane **

The **stresses generated** in gantry girders due to the above loads are more than those affected by **gradually applied loads.**

This is due to the forces established by the sudden **application of brakes** to the quickly moving loaded cranes acceleration, **retardation, vibration, feasible slip of slings, **etc.

The **steelwork **which takes these **quick-acting cranes** must be heavier than the **steelwork **which supports the **slow-moving cranes**.

With quick-acting **electric overhead traveling** (**E.O.T**) cranes, the stresses in the gantry girders are generated almost **instantaneously**, whereas, with slow-moving **hand-operated** cranes, the bending stresses in the girder are generated gradually from **zero up **to their ultimate values.

- Additionally, impact loads on cranes
**(IS : 875)**

Sr. No. | Types Of Load | Impact Allowance (%) |

(A). | Vertical loads Transferred | |

(i) | For electric operated cranes | Allowance of 25 % from the maximum static wheel load. |

(ii) | For the hand-operated cranes | Impact Allowance of 10% of the tatal static wheel load. |

(B). | Horizontal Forces Are Transverse (Surge load) To The Rails | |

(i) | For electric operated cranes | Allowance around 10 % of the weight of the crab plus the weight lifted on the crane. |

(ii) | For the hand-operated cranes | Allowed 5 % of the weight of the crab and the weight lifted on the crane. |

(C). | Horizontal Forces Along The Rails (Braking Load) | |

(i) | For electric operated cranes | 5 % of the calculated static wheel loads. |

(ii) | For the hand-operated cranes | 2.5 % of the static wheel loads. |

### 3. Longitudinal Horizontal Force (Drag Force)

This is caused due to the starting and stopping of the crane girder moving over the **crane rails**, as the crane girder moves **longitudinally,** for example, in the direction of the gantry girder.

This force is also known as **Braking Force** or **Drag Force. **This force is taken equal to **5%** of the** static wheel loads **for the **electrically operated** cranes or hand-operated cranes.

### 4. **Lateral Load (Surge Load) **

Lateral forces on crane girders may be induced by the,

**A) Lateral forces are caused due to the sudden starting or stopping of the crab when moving over the crane girder.**

- As with the longitudinal
**gantry girders**, the**frictional resistance**of the**rail**is transmitted into the c**rab girders**and from them into the crosshead girders, thence, as point loads through the**major wheels**, into the**top**or**compression flanges**of the gantry girders. - The positions of the major wheels when maximum
**lateral bending**and**shear**take place on the gantry girder will be similar to those when a maximum v**ertical bending**moment and shear occurs.

**B) Lateral forces are similarly caused when the crane is dragging weights across the floor of the shop.**

- The crane is always requisitioned to
**drag weights**across the**shop floor**. If the load is greatly massive, it is generally mounted on roughly**fashioned rollers**, probably moving on a**timber plank path**. - The
**lateral thrust**and pull on the**compressive flanges**of the gantry girders, therefore, become a matter of**conjecture.** - The
**resisting forces**are, firstly, the friction of the major wheel walks upon the**gantry rails**and, secondly, the**forces**given by the**flanges**of the major wheels bearing against the**gantry rails.** - The
**lateral thrust**is supposed to act in the plane of the**center of gravity**of the**upper flange**. Working as it does at the**rail level,**it has a**lever arm**generating torque. - This small
**lever arm**and, therefore, the**torque**are**omitted**. No support is assumed to be afforded by the lower or**tensile flange**in resisting**lateral thrust.** - Nonetheless, should this help be examined, then the
**torque**due to the**thrust multiplied**by the distance from the**line of action**of the thrust to the N.A.

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**Uses Of Gantry Girder **

The following are **Gantry Girder uses,**

- To understand the
**behavior of gantry girders**. - To
**calculate the different loads**acting on the gantry girder. - To
**compute**the maximum**bending momen**t and maximum**shear force**in the girders. **Choose**the appropriate**cross-section**s for gantry girders.**Design suitable connections**.

**Characteristics Of Gantry Girders **

- The design of the gantry girder is a specific example of a
**laterally unsupported beam.** - It is subjected to in extension to
**vertical loads**and**horizontal loads**along and perpendicular to its axis. - Loads are
**dynamic**and**generate vibration.** - The
**compression flange**needs critical attention.

**Gantry Girder Design Example**

The design of the gantry girder is a trial and error procedure. In the design, it is assumed that

- Lateral load is resisted entirely by the compression flange with plates, channels, etc.
- The vertical load is resisted by the entire beam.

### Design Steps

**1. Maximum Wheel Load **

The first step is to determine the maximum wheel load of the crane girder transferred to the gantry girder.

**U.D.L. on crane girder = **Total weight of crane girder/ Span of crane girder

**Concentrated load =** weight lifted by hook + weight of the trolley

This** concentrated load** is placed at the point of the minimum** hook approach** and the maximum **reaction of the crane girder** is computed. At each end of the crane girder, there are two wheels.

**Load on each wheel =** Maximum reaction / 2. This wheel load is increased by** 25%** for impact and then factored.

**2**. **Maximum B.M. In The Gantry Girder **

**U.D.L. on gantry girder =**Self-weight of gantry girder + weight of rail section

For **maximum B.M.**, the **wheel loads** should be so placed that the **C.G.** of the two-wheel loads (R) and one of the wheel loads lie **equidistant **from the center of the span (C). The **maximum B.M.** will then occur under that wheel load which is nearer to the **center of the girder. **

**3. Maximum Shear Force **

**U.D.L. on gantry girder =**self-weight of gantry girder**+**weight of rail section. The**S.F.**due to the wheel load is ultimate when one of the wheels is at the support.

**Horizontal Force (Drag Force) Braking Force**

It is taken equal to **5%** of the **static wheel load** on each gantry girder. This load is factored in.

**Horizontal Transverse Force (Surge load)**

**Surge load =** 10% of (weight lifted on hook + weight of crab) For one crane this load is shared by four wheels.

**Surge load on each wheel**= Total surge load / 4. This load is also factored in.

**4. Section Selection For Gantry Girder **

Generally, an** I-section **with a channel is chosen, though an I-section with a plate at the **top flange** may be used for **light cranes.**

Generally, the following guidelines are followed.

**Economic depth of girder** = L/12

**Width of flange = **L/40 to L/30

Zp required = k. Mu/Fy

= 1.40 Mu/Fy

The moment capacity for vertical loads should be about **40 to 50% higher** (k = 1.4 to 1.5) than the moment due to vertical loads so that the section can resist combined **horizontal **and v**ertical moments** safely.

**5. Calculate the Izz, Iyy and zpof trial section selected**

**6. Check for moment capacity.**

**Md** should be greater than **Mu**. The top flange should be examined for bending in both axes utilizing the interaction equation.

**7. Check For Shear Capacity **

**Maxi. S.F. =**Vz

Shear capacity,

**0.6 Vd** should be **greater than Vz**.

**8. Check For Buckling Resistance **

When the gantry girder is laterally not supported, the design bending strength of the beam is given by,

**Md** should be more than **Mu**.

**9.** **Check For Local Buckling**

At points of **concentrated load **(wheel load or reactions) the web of the girder must be checked for **local buckling** and, if necessary, **load-carrying stiffeners** must be provided to prevent local buckling of the **web**.

**Bulking Resistance =**

**Buckling resistance** must be more than maximum **factored wheel load**.

**10.** **Weld Design **

Required** shear capacity **of weld, **Weld **is required to connect the channel to the top flange of the **T-beam**.

The capacity of 1 mm long weld.

**P=**

= 0.7s

For shop welding,

= 1mm

**If P>â€¦. **Safe.

**11.** **Check For Deflection**

Maximum deflection at center for two-wheel loads,

**Permissible Deflection**

For EOT crane up to 500 KN Capacity,

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**Limiting Deflection Of Gantry Girder **

The maximum vertical deflection of the gantry girder shall not exceed the following values.

Sr. No. | Category | Maximum Deflection |

1. | Vertical Deflection | |

i) | Manually operated cranes | L / 500 |

ii) | EOT cranes up to 50 t (500 KN) | L / 700 |

iii) | EOT cranes over 50 t (500 KN) | L / 1000 |

| ||

2. | Lateral Deflection | |

i) | Relative between rails | 10 mm or L / 400 |

**Gantry Girder Sections **

**Small cranes** may contain an **integrated double beam **unit.** Large cranes** consist of a **double truss** unit. The figure indicates the types of** beam sections** utilized for the **gantry girder**.

These beams are subjected to** vertical and horizontal loads **due to the **dead load **of the crane, the **hook load,** and **dynamic loads**. Since they are similarly subjected to **horizontal loads** a larger top flange is mainly provided.

For a **light gantry girder**, a **universal beam** simply or a **universal beam** with a channel connected to the top flange is utilized. A **heavy gantry girder** contains a **plate girder** along with a surge girder.

The figure below indicates the** types of rails **which are fixed to the **top flange** of the **gantry girder**.

The rails over the gantry girder are firmly fixed to the girder by **bolted clamps** or **hook** at a **spacing of 0.50 meter to 1 meter** to prevent the rail from **lateral dislocation **due to **lateral forces**.

## FAQs

### Gantry Girder

TheÂ **Gantry Girders**Â are girders that support the loads that are conveyed through the**Â **traveling wheelsÂ of the crane. TheÂ **gantry girderÂ **spans between the**Â bracketsÂ **connected toÂ **columns**, which may either be ofÂ **steel or reinforced concrete.**Â Thus

### Crane Girder

**Crane GirdersÂ **are the girders that carry hand-operated orÂ electrically operated**Â **overhead cranes industrial buildings such asÂ factories, workshops, steelworks,Â etc. to lift heavy materials, equipment, etc., and to take them from one location to the other, within the building.Â

### Web Plate

**Web stiffeners**Â can be explained as the pairs of small blocks, cut out from panels that are usually nailed to the joist webÂ in order to stiffen a deepÂ web, which increases the reaction capacity or can accommodate a special connector.

### Where is gantry girder used?

Gantry Girder is used at aÂ manufacturing plant, to efficiently provide an overhead traveling crane to transportÂ heavy componentsÂ ofÂ machinesÂ from one place to another place.

### What is the difference between a plate girder and a gantry girder?

Steel Beam comprised of plates is generally called the Plate Girder, however, Gantry Girder is one that supports the loads that are conveyed through the traveling wheelsÂ of the crane.

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