AGE 409

INTRODUCTION TO AGRICULTURAL STRUCTURES DESIGNS. (3 Units)

Course Lecturers: Prof. E.B. Lucas/ Engr. P.O.O. Dada

Course Outline

Introduction to agricultural structures. Selection of materials in relation to use – steel, wood, concrete and

masonry. Types of structural frames. Estimating loads, stress analysis. Introduction to structural design.- philosophy of design elastic and plastic design concepts. Reinforced concrete design. Design for axial loadings. Design of beams, foundation, slab, columns, connections and joints. Computer concept for improved analysis and design. Design project.

Introduction to Structural Analysis

Three phases are recognized in a structure on Engineering project. They include:

Planning- factors affecting the layouts and dimensions

-- answer basic questions

-- aesthetics

- sociological, legal, economic and environmental

- construction requirement affecting type of structure to be selected

Design- consideration of alternative solution involved in planning phase

- choice dependent on economic and constructional features

- aspects of competitive bidding.

Construction- procurement of materials, equipment and personnel

- fabrication of members and sub-members

- transportation to site

- field construction and erection

Types of structural frames

Beams and Columns Truss Arches Rigid frames Cylindrical tank Retaining wall

Types of Support

Hinge support Roller support Free end or movable roller support Hinged immovable or fixed end support Built-in end support

Structural Analysis

Types of loads:Dead loads – stationaryLive loads – moving

Stress = F/A

Strain = Extension/lengthFactor of safety (N) = ultimate stress/ design stress

Livestock Structures: A facility primarily designed and constructed or remodeled to house animals with the overall aim of increasing productivity.Livestock: Domesticated animals kept under human control. Examples include: Dairy cattle, pigs, sheep, goats, horses and poultry

Objectives of keeping LivestockFood supply source

Raw materials

Manure supply

Transportation

Religion and culture

Social aspects

Sport and recreation

Employment and income

Benefits of Livestock Structures Reduction of drudgery Protection for animals Individual and national benefits

Environmental factors affecting animal performance Temperature Relative Humidity Ventilation Light Heat and Moisture

Livestock Structure (Case Studies)

Poultry, cattle and swine: Poultry:

Site selection: The site must be well drained and be in a good location. It must be near to sources of adequate water which must be in good quality and quantity.Ventilation must be adequate and protected from strong windsProvision of foot-dips at entrances, wire netting and trenches where applicableDisease control must be achieved by good sanitation and medical facilities.

Construction details: The poultry house must be aligned in the east-west direction.Floors may be made from gravel or well drained soil or concreteRoofing materials can include corrugated metal sheets (cheap, durable)Construction should be in done to aid sanitation and proper disposal of waste, dead birds etc.

Examples of Livestock Structures

Shed and yardsBattery cageBarnsHen basketDeep litter house

Crop Storage Structures: Container or unit designed and fabricated to perform the function of safely keeping crops

Justification of crop storage• Seasonal variation• Seeds for next planting season• Economic considerations• To avoid social unrest• Protection from deterioration

Classification of Crop Storage Structure• Improvised (indirectly used) eg. Baskets, earthen pots, drums, calabashes.• Traditional (Indigenous) eg underground pits, rhumbu, platforms, ,cribs and

poles.• Modern (results of research) eg. Silos, warehouse, evaporative coolers

Silos

Technical Aspects of silos:

Silos can be classified into deep and shallow and this is done on the basis of the following:

a) Plane of rupture method

b) Equivalent diameter method

c) Height to lateral dimension method

Pressure in silos:

Rankine’s equation:2

45(tansin1

sin1 2

wyL

Ventilation

Ventilation: circulation of air between an enclosure and it’s surroundings. It could be free (natural) or forced (mechanical means).

Factors to consider when designing for good ventilation include: Amount of heat and moisture generated Amount of heat and moisture to be exchanged Amount of air required to achieve the above Method of supply and desired quantity of air to introduce.

Natural ventilation V= AESV is Volume of air flow (m2/s)A is area of inlet openingE is effectiveness of opening (0.35-1.0 for perpedicular

winds and 0.4-0.6 for diagonal windsS is wind velocity (m/s)

Heat Exchange

Temperature of an enclosure is a reflection of the amount of heat present in the enclosure.

Heat may be added or removed and air is the medium of exchange.

Mn = mass of dry air(Kg/hr)

hi = Enthalpy of incoming air as ambient temp. (KJ/kg of dry air)

ho = Enthalpy of out going air at conditions inside the enclosure(KJ/kg of dry air)

Heat exchange is a function of the insulating value of the building components while moisture exchange depends on vapour permeability.

hiho

QtMn

Beams:A beam is a structural member used to resist load acting across its longitudinal axis

It is designed to resist:

1. Bending moment

2. Transverse/Vertical shearing forces

3. Deflection

Could be wooden, steel or concrete beams.

Design of wooden beams should take the following into consideration: Bending/ shear stresses Deflection Prevention of lateral buckling

d/b < 3 for lateral stability and position of centriod

DeflectionA deformation that accompanies the bending of a beamBending deflectionShearing deflection

Deflection of beam is dependent on: Type of loading Supports Span Modulus of elasticity of material of construction Maximum deflection

where W = load per unit length

L = Span

E = modulus of elasticity

EI

WLb

384

5 4

Design of Steel beams

Involves the following steps:

Estimation of load to be sustained Compute the maximum bending moment and section modulus Compute the shear stress

For rectangular steel beam, maximum shear stress is

A

V5.1max

Columns

A vertical structural member subjected to axial compression loading.

Used where overhead loads are to be carried

Classified as long, intermediate or short depending on the span to depth ratio.

Short columns fail by yielding

Long columns fail by buckling

Slenderness Ratio: (Important parameter in design) is the ratio of the effective length to the least lateral dimension.

Wooden columns could be Single load timber Solid timber with lamination of planks Open column composed of planks but separated by spaces

Design Concepts

The FAO and Leonhard Euler method

Materials of Construction

Engineering properties of construction materials are broadly grouped into the following:

Physical – bulk density, specific gravity, porosity, void ratio, permeability, colour, size, shape and smell

Mechanical- tensile and compressive strength, modulus of elasticity, rupture, shear strength, hardness, impact, endurance and creep behavior

Thermal- thermal conductivity, expansion, contraction and specific heat

Chemical- Acoustical-

Engineering properties

StrengthDurabilityResistance to corrosionHardnessToughnessResilienceWorkabilityDimensional stability

Choice of Construction Materials

Selection depends on: Type and functions of the building and specific characteristics Adequacy of relevant properties Ease of handling Appropriateness Ease of site adjustment Economic aspects of the building in terms of original investment Availability of the materials in the area Availability of skilled labour Quality and durability of different materials Cultural acceptability

Types of construction materials

Earth: Advantages and disadvantagesNatural fibres- bamboo, leaves, sisal Wood and wood productsConcrete –cement, aggregates,water

Computer in Design

Facilities: De-skilling the operation Simulation and optimization Computer aided drafting

AdvantagesVery fastAccurateGreater scope and limitedCan be modified

Use of Computer in Design

Computer aided design (CAD)Computer aided manufacturing (CAM)

Recommended Textbooks

1. Farm structures in tropical climates by L.P. Bengtnos and J.H. Whitaker (FAO)

2. Agricultural buildings and structures by J.H. Whitaker

3. Mid west plan service- structures and environmental handbook