Week 3 Challenge

1. 1. State the primary load cases to be considered for design.

Ans-

• Dead Load (IS 875: Part I)
• Live Load (IS 875: Part II)
• Wind Load (IS 875: Part III)
• Snow Load (IS 875: Part IV)
• Seismic Load (IS 1893: 2016)

1. 2. What is One Way slab?

Ans-

A one-way slab is a reinforced concrete slab used in construction, primarily for building floor and roof structures. It is called "one-way" because it is designed to primarily resist loads in one direction, usually along the shorter span of the slab. This design is most suitable when the longer span of the slab is supported by walls or beams that can effectively distribute the load in that direction.

The primary reinforcement bars, also known as the main bars or simply the "bottom bars," are placed in the direction where the slab is expected to carry the majority of the load. These bars are usually placed near the bottom of the slab's depth to provide tensile strength and resist bending due to the imposed loads. In the perpendicular direction, secondary reinforcement, often in distribution bars, is provided to distribute loads effectively.

1. 3. What is the value of the unit weight of structural steel and soil?

Ans-

1. Structural Steel: The unit weight of structural steel can vary based on the composition and type of steel. Generally, the density of steel is around 7850 kg/m³ (or 0.2836 lb/in³). However, this value can change slightly depending on the alloying elements and manufacturing processes used. It's important to note that different types of structural steel, such as carbon steel, stainless steel, or alloy steel, might have different densities.

2. Soil: The unit weight of soil can vary significantly depending on the type of soil, its moisture content, compaction, and other factors. Different types of soil like sand, clay, silt, and gravel have varying densities. Generally, the unit weight of soil falls within the range of 1500 to 1900 kg/m³ (or 47 to 119 lb/ft³). However, these values can change widely based on the factors mentioned above.

1. 4. Name a few sections that can be defined using the Properties tab in STAAD Pro.

Ans-

1. Beam Sections: Beam sections define the cross-sectional shape and dimensions of beams. Examples include I-sections, T-sections, rectangular sections, circular sections, etc.

2. Column Sections: Column sections define the cross-sectional shape and dimensions of columns. Examples include rectangular sections, circular sections, H-sections, etc.

3. Bracing Sections: These sections are used for bracing members within a structure. They can have various shapes and dimensions.

4. Truss Sections: Truss sections are used to define the properties of truss members. They can be different from the beam and column sections.

5. Plate Sections: Plate sections define the properties of plates, such as thickness and material properties. These are often used for analyzing and designing plate elements like slabs or walls.

6. Shell Sections: Similar to plate sections, shell sections define the properties of shell elements, which are used to model surfaces of structures like walls, roofs, and shells.

7. Solid Sections: Solid sections are used to define the properties of solid elements in 3D modeling. These are often used to model concrete or other solid materials.

8. Foundation Sections: These sections are used to define the properties of foundation elements, such as pile sections or mat foundations.

9. Rebar Sections: In reinforced concrete design, rebar sections define the properties of the reinforcement bars used in concrete members.

10. Cable Sections: Cable sections define properties for cable elements used in tension structures like suspension bridges or cable-stayed structures.

11. User-Defined Sections: Some software, including STAAD.Pro, allow you to define custom or user-defined sections that might not fall into standard categories.

1. 5. Define Primary Beams.

Ans-

Primary beams, also known as main beams or primary framing members, are structural elements that play a critical role in supporting the loads and maintaining the integrity of a structure. They are key components in a structural system and are designed to carry the majority of the applied loads, such as dead loads, live loads, wind loads, and other loads that act on a structure.

2. 1. State the factors and parameters that influence the design pressure intensity of a high-rise building.

Ans-

1. Wind Loads: Wind is one of the primary external forces acting on a high-rise building. The design pressure intensity is influenced by the wind speed, directionality, turbulence, and the building's height and shape. Wind tunnel testing and computational fluid dynamics (CFD) analysis are often used to determine wind loads accurately.

2. Building Height and Shape: Taller buildings are subjected to higher wind pressures due to increased exposure to wind at greater heights. The shape of the building also affects how the wind interacts with it, leading to varying pressure distributions.

3. Location and Surroundings: The geographical location of the building plays a role in determining the design pressure intensity. Buildings in coastal areas, open terrains, or urban environments experience different wind patterns and intensities.

4. Local Building Codes and Standards: The applicable building codes and standards guide design loads, including wind pressures. These codes account for regional variations, climate conditions, and safety requirements.

5. Structural System: The structural system of the building, including its framing, load-bearing elements, and overall stiffness, affects how wind loads are distributed and absorbed. Different structural systems handle wind loads differently.

6. Exposure Category: Buildings are classified into different exposure categories based on their surroundings and proximity to other structures or obstacles. The exposure category influences the design pressure intensity by considering the terrain roughness and shielding effects.

7. Occupancy and Usage: The purpose of the building and its occupancy category can impact the design pressure intensity. Buildings with specific functions like hospitals or critical facilities might have stricter design requirements.

2. 2. Mention the load transfer process of a Reinforced Concrete Building.

Ans-

The load transfer process in a reinforced concrete building involves the distribution of various loads from the superstructure (floors, walls, roofs) down to the foundation through a series of structural components.

Load> Slab> Secondary Beams> Primary Beams> Column> Foundation> Ground (Soil/Hard Strata)

3. 1. Differentiate One-Way and Two-way slabs. Elaborate on each slab type.

Ans-

One-Way Slab: A one-way slab is a type of reinforced concrete slab that primarily spans in one direction, meaning the main reinforcement bars are placed in one direction only. One-way slabs are typically supported on two opposite sides by beams or walls. These slabs are designed to carry loads in a single direction, which is usually the longer span of the slab.

Key features of one-way slabs:

1. Load Distribution: The primary load-carrying direction is along the longer span of the slab. The loads are transferred to the supporting beams or walls through the main reinforcement bars in this direction.

2. Main Reinforcement: The main reinforcement bars, also known as the bottom bars, are placed along the longer span of the slab. These bars resist the tensile forces that develop due to the bending moments in that direction.

3. Secondary Reinforcement: Additional reinforcement, known as distribution bars or links, is provided perpendicular to the main reinforcement to distribute the loads evenly and prevent cracking.

4. Support: One-way slabs are typically supported on two opposite sides, either by beams or load-bearing walls. The beams or walls provide support along the shorter span.

5. Span-to-Depth Ratio: One-way slabs usually have a larger span-to-depth ratio in the shorter span direction, which helps optimize structural efficiency.

Two-Way Slab: A two-way slab is a type of reinforced concrete slab that spans in both directions, meaning it is supported on all four sides. In two-way slabs, the main reinforcement bars are provided in both directions to resist bending moments and shear forces.

Key features of two-way slabs:

1. Load Distribution: The loads are distributed in both directions, making it suitable for square or rectangular shapes. The loads are transferred to the supporting columns or walls in both longer and shorter spans.

2. Main Reinforcement: Main reinforcement bars are provided in both directions, forming a grid-like pattern. This helps the slab resist bending moments in both directions.

3. Shear Reinforcement: Due to the two-way action, two-way slabs experience shear forces in both directions. Shear reinforcement, such as stirrups or shear links, is provided to enhance shear capacity.

4. Support: Two-way slabs are supported on all four sides, typically by columns or walls. The loads are distributed to all the supports.

5. Span-to-Depth Ratio: Two-way slabs usually have a smaller span-to-depth ratio compared to one-way slabs. This is due to the need to distribute the loads in both directions effectively.

3. 2. Explain the concept of secondary beams with a proper sketch.

Ans-

The secondary beams are primarily connected to the primary beams mainly simply supported beams.

• The secondary beams are provided for the better distribution of slab loads along with the primary beams which rest on the slabs.
• So mainly the secondary beams are the beams that are not directly connected to the columns. The secondary beams rest on the other beams that are directly rest on the column and those beams are known as the primary beams.
• So the secondary beams carry a certain amount of total load and help them to distribute the loads in the respective manner.
• In secondary beams, it is important to release the end moments at the supports, because of this all the secondary beams are provided with the pinned connection.

Diagram-

3. 3. Mention the Primary load cases.
a. State the Indian Standards for each load case
b. Detail the parameters of each load case
c. Brief each load case

Ans-

a. State the Indian Standards for each load case:

• Dead Load (IS 875:Part 1).
• Live Load (IS 875:Part 2).
• Wind Load (IS 875:Part 3).
• Snow Load (IS 875:Part 4).
• Earthquake Load (IS1893:2016).

b. Detail the parameters of each load case:

• Member Loads.
• Concentration Loads.
• Floor Loads.
• Plate Loads.

c. Brief each load case:

Dead Load:-

• The dead load is defined as the continuous load in a structure i.e. the load of the machine etc and this load is caused by the weight of the members that are permanently attached to the particular structure.
• The dead load of the structure comprised of the load of the column, load of the beam, loads of the floor slab, roofing, walls, the load of windows, or maybe the load of the electrical fixture. All the loads which are permanent on the structure are called the dead load of the structure.

Some of the Dead Load(Unit Weight) of the following materials:

• Cement : 1440 Kg/cu.m.
• Steel: 7850 Kg/cu.m.
• Sand: 1600 Kg/cu.m.
• Concrete : 2400 Kg/cu.m.
• RCC: 2500 Kg/cu.m.
• Soil: 1800 Kg/cu.m.

The dead Load factor is 1.

Live Load:-

• Live loads are the loads that fully or partially vary from time to time on the structure.
• Live loads are not constant loads throughout the life span of a structure.
• Live loads may vary from time to time according to their usage or occupancy.
• The live load may vary depending on the type of structure such as a residential building, commercial building, industrial building etc.
• For residential buildings, we use 3KN/sq.m Live Load.
• Live loads on floors and roofs consist of all loads which are temporarily placed on the structure. Some of the live loads (Unit Weight) are:

• All rooms and kitchen: 2 KN/sq.m.
• Bathrooms and Toilets: 2 KN/sq.m.
• Balcony : 3 KN/cu.m.
• Staircase/Corridors : 3 KN/cu.m.

Wind Load:-

• A wind Load is a force on a structure that is arising from the impact of the wind. Wind load is an important load case for the structure. We considered this type of load where the structure is situated or located in the hilly areas of the mountain areas where we can expect high speed of the winds that can affect the structure. In those areas, we need to consider the wind loads.
• Mainly we calculated the wind loads for the roofs of the structure.

Earthquake Load:-

• Earthquake loads or seismic loads are also important load case that needs to be considered while designing and analyzing the high-rise structure of the building.
• Mainly we considered this type of load where there are high chances of earthquakes or we can say we have to consider this load in the earthquake-prone areas, where there is a high risk of earthquakes.
• And according to the codal provision, the dynamic seismic analysis can be carried out via any of the two methods and these two methods are spectrum analysis and time history analysis.

3. 4. Detail the steps involved in assigning Properties and Support to a model using STAAD Pro sequentially.

Ans-

1. Open or Create a New Model:

   • Launch STAAD.Pro software.
   • Open an existing model or create a new one by defining nodes, members, and other structural components.

2. Assign Properties:

   • Click on the "Properties" tab in the left panel of the STAAD.Pro window.

3. Define Material Properties:

   • Click on the "Materials" option to define the properties of the materials used in the structure (e.g., concrete, steel).
   • Specify material properties like Young's modulus, Poisson's ratio, density, etc.

4. Define Section Properties:

   • Click on the "Sections" option to define the cross-sectional properties of the structural members.
   • Select the type of section (I-section, T-section, etc.).
   • Enter the dimensions and other relevant properties of the selected section.

5. Assign Section to Members:

   • Go to the "Structure" tab.
   • Select the members you want to assign sections to by clicking on them.
   • Right-click and choose "Assign > Section" to assign the previously defined section properties to the selected members.

6. Assign Support Conditions:

   • Click on the "Supports" option to assign boundary conditions to the nodes of the structure.
   • Select the nodes where support is needed.
   • Choose the appropriate support types, such as fixed, pinned, roller, etc., for each node.

3. 5. Brief the steps to be followed to create and assign secondary beams in STAAD Pro.

Ans-

The steps that are involved in creating and assigning the secondary beams in STAAD Pro are discussed below:

• First, create a simple model by using the node in STAAD pro
• Click on the create beam option and create a beam in the direction of the X and Z axis
• Right Click on the primary beam in the section
• Right-click and add Add node at the mid on the beam section a node will be added
• Click on the create beam to draw the beam along mid of the bay

Practical
1. Calculate the wind pressure for the given building
a. Building Dimension : 20m x 30m x 20m height RCC
b. Building usage: Hospital block in city center
c. Location: Darjeeling
2. Calculate the Dead load and Live load for the above building with reference to IS standards ( assume suitable sections )

1. Calculate the wind pressure for the given building a. Building Dimension : 20m x 30m x 20m height RCC b. Building usage : Hospital block in city centre c. Location : Darjeeling
Ans-
Building dimensions:- 20m * 30m * 20m. Buidling usage:- Hospital Block. Location of the building:- Darjeeling.
Step-1
We know the formula to calculate the design wind speed,that is: Vz=Vb⋅k1⋅k2⋅k3⋅k4 where, Vb = Basic Wind Speed (m/sec). k1 = Risk Co-efficient. We can find the value of risk co-efficient, k1 from IS code 875:Part 3 2015, Table 1). k2 = Terrain Roughness and Height Factor. k3= Topography Factor. We can find the value of topography factor from IS cide 875:Part 3 2015 clause no 6.3.3. k4 = Importance factor.
From Is Code			Calculation			Height (in m.)	K1(Impotant Building) Table-1	K2 Table-2	K3 Clause 6.3.3.1	K4 6.3.4	Vz (in m/s)	Pz (in N)	Pz (in KN)
Vb	47	m/s	Vz=Vb⋅k1⋅k2⋅k3⋅k4	M/S		10	1.07	0.8	1.36	1.00	54.71552	1796.273	1.796
K1	1.07		54.71552	M/S		15	1.07	0.8	1.36	1.00	54.71552	1796.273	1.796
K2	0.8		Pz=0.6⋅(Vz^2)	N		20	1.07	0.8	1.36	1.00	54.71552	1796.273	1.796
K3	1.36		1796.272877	N
K4	1		1.796272877	KN		Basin wind Speed ofa Darjeeling(Vb)			47	M/S	Terrain	4
2. Calculate the Dead load and Live load for the above building with reference to IS standards (Assume suitable sections).
Assumtions
Size (in m.)			Item Details	Nos.
L	B	D
20	30	0.15	Slab (Concrete)	2
10	0.3	0.3	Beam (Concrete)	6
0.3	0.25	3	Column (Concrete)	6
0.25	10	3	Brick Wall	6
			Total Volume of Concrete Used	186.75	Cum
			Total Volume of Brick Masonary Used	45	Cum
			0.2% Steel used in Concrete	0.3735	Cum
			Unit Weight of Steel bar of Size 12 mm	0.89	Kg/m
			Total length of Bar used	3303.088	m
			Total weight of Bar used	2939.748	Kg/m
			Total load Due to Steel	28.80954	KN	A
			Unit weight of RCC	25	KN
			Total load due to All RCC	4668.75	KN	B
			Unit weight of Brick Masonary	18	KN
			Total load due to Brick Masonary	810	KN	C
			Total Dead Load of the structure	5507.56	KN	A+B+C
			OCCUPANCY LIVE LOAD For ward rooms,dressing rooms,dormitories and lounges= 2.0KN/m^2 Kitchen and Laboratory 3.0KN/m^2 Dining room and Cafeteria 3.0KN/m^2 Toilets and Bathrooms 2.0KN/m^2 X-ray rooms and Operating Rooms 3.0KN/m^2 Office and OPD Room 2.5KN/m^2 Corridor and Passages 4.0KN/m^2