As per IS 456 : 2000, the minimum beam width required for a reinforced concrete beam, for 2 hours of fire exposure is:
200 mm
Understanding IS 456:2000 Fire Resistance Requirements
The question asks about the minimum width required for a reinforced concrete beam according to IS 456:2000, specifically for a fire exposure duration of 2 hours. Concrete structures are designed not only for strength and serviceability but also for fire resistance to ensure the safety of occupants and prevent structural collapse during a fire event.
IS 456:2000 is the Indian Standard Code of Practice for Plain and Reinforced Concrete. It provides guidelines for various aspects of concrete design and construction, including provisions related to fire resistance.
Minimum Beam Width for Fire Resistance as per IS 456:2000
Annex A of IS 456:2000 deals with the Fire Resistance of Concrete Structures. This annex provides minimum dimensions for concrete members like beams, slabs, columns, and walls, along with minimum cover requirements, to achieve specific periods of fire resistance.
Table A.1 in IS 456:2000 provides the minimum dimensions of flexural members (like beams) and compression members (like columns) to achieve fire resistance ratings from 0.5 hours up to 4 hours.
Let's look at the requirements for flexural members (beams) based on the desired fire resistance period:
| Fire Resistance (minutes) | Fire Resistance (hours) | Minimum Beam Width (mm) |
|---|---|---|
| 30 | 0.5 | 80 |
| 60 | 1 | 120 |
| 90 | 1.5 | 150 |
| 120 | 2 | 200 |
| 180 | 3 | 200 |
| 240 | 4 | 240 |
According to this table from IS 456:2000, for a fire resistance period of 120 minutes (which is equal to 2 hours), the minimum required width for a reinforced concrete beam is 200 mm.
Detailed Analysis of Options
Now let's compare the options provided with the requirement from IS 456:2000 for 2 hours of fire exposure:
- Option 1: 250 mm. This is greater than the minimum required 200 mm.
- Option 2: 200 mm. This exactly matches the minimum requirement from the code for 2 hours.
- Option 3: 300 mm. This is greater than the minimum required 200 mm.
- Option 4: 150 mm. This is less than the minimum required 200 mm for 2 hours fire resistance. According to the table, 150 mm is the minimum width for 1.5 hours fire resistance.
Therefore, the minimum beam width required for a reinforced concrete beam for 2 hours of fire exposure, as per IS 456:2000, is 200 mm.
Revision Table: Key Dimensions for Fire Resistance
| Fire Resistance Duration | Minimum Reinforced Concrete Beam Width (IS 456:2000) |
|---|---|
| 0.5 hours (30 min) | 80 mm |
| 1 hour (60 min) | 120 mm |
| 1.5 hours (90 min) | 150 mm |
| 2 hours (120 min) | 200 mm |
| 3 hours (180 min) | 200 mm |
| 4 hours (240 min) | 240 mm |
Additional Information on Concrete Fire Resistance
Fire resistance of concrete members depends on several factors, including:
- Minimum Dimensions: As seen in the table, minimum width and depth (not shown here but also specified in the code) are crucial. Larger dimensions generally provide better fire resistance.
- Concrete Cover: Adequate concrete cover to the reinforcement bars is essential. The cover protects the steel from reaching critical temperatures quickly, which would cause it to lose strength and buckle. IS 456:2000 also specifies minimum cover requirements for fire resistance in Table A.1.
- Aggregate Type: The type of aggregate used in the concrete mix affects its performance under high temperatures. For example, concrete made with siliceous aggregates might spall more readily than concrete made with calcareous aggregates.
- Member Type: Beams, slabs, columns, and walls have different fire resistance characteristics and thus different minimum dimensional requirements.
- Load Conditions: The load on the member during a fire can also influence its fire resistance.
Adhering to these minimum requirements in IS 456:2000 helps ensure that concrete structures can withstand fire for a specified duration, allowing for safe evacuation and reducing potential structural damage.
Important Questions from Introduction
In the following table, the left column contains the names of standard graph algorithms and the right column contains the time complexities of the algorithms. Here, n and m are number of vertices and edges, respectively. Match each algorithm with its time complexity.
List I List II Standard graph algorithms Time complexities A. Bellman‐Ford algorithm I. O(m*log n) B. Kruskal’s algorithm II. O(n 3) C. Floyd‐Warshall algorithm III. O(n*m) D. Topological sorting IV. O(n + m) Choose the correct answer from the options given below :
How many cards must be selected from a standard deck of 52 cards to guarantee that at least three hearts are present among them?
Match List 1 with List 2 and choose the correct answer from the code given below:
List I
(Graph Algorithm)
List II
(Time Complexity)
a) Dijkstra’s algorithm
i) Θ(E log E)
b) Kruskal’s algorithm
ii) Θ(V 3)
c) Floyd-Warshall algorithm
iii) Θ(V 2)
d) Topological sorting
iv) Θ(V + E)
Where V and E are the number of vertices and edges in graph respectively.
The solution of recurrence relation: T(n)=2T(sqrt(n)) + lg(n) is
Modulus of elasticity of concrete, E is calculated using:
