Reticular Concrete Structures In Situ

Reticular Structures of Concrete Executed In Situ

• This document discusses reticular structures of concrete executed in situ designed for teaching purposes and features images from web platforms.
• The document explicitly prohibits any reproduction on student documentation forums or other platforms.

Introduction

• Reinforced concrete offers advantages and disadvantages when compared to other materials like steel used in construction, such as versatile design and durability,.
• Structures built in situ have rigid nodes and high durability if protected, especially corrosion resistant steel.
• They offer high fire resistance, but take longer to execute due to the need for formwork, reinforcement, pouring, and hardening.
• They feature elevated weight, high resistance to horizontal forces, and are economic for buildings up to 15 stories.
• Prefabricated structures can resolve the problem of long execution times.
• Reinforced concrete reticular structures typically have rigid nodes and is hyperstatic, unless complex designs are used.
• Girders transmit compressive and flexural loads to supports, which are subjected to compound compression with moments in opposite directions in the support’s halves.
• Supports have compressed and tensioned zones when subjected to gravity loads.

Support Typologies in Reinforced Concrete Structures

• Reinforced concrete columns usually have square, rectangular, cylindrical or chamfered sections.

Support Sections

• In-situ columns are commonly square or rectangular, with a minimum side dimension of 25 cm (30 cm in seismic zones), increasing in 5 cm increments.
• Polygonal, circular sections, or pilasters with curved ends may also be used.
• T or I geometries can reduce material consumption when embedding two enclosures despite being less common.
• Main reinforcement includes at least four bars or polygonal sections and a bar in each corner, with at least four longitudinal bars in circular columns.
• In seismic areas, a minimum of three longitudinal bars are required on each side of the support, spaced no more than 15 cm.
• Longitudinal reinforcement should have a minimum diameter of 12 mm and be arranged symmetrically, working in tension and compression.
• Transverse reinforcement like hoops or stirrups secure longitudinal bars and prevent buckling due to compressive stress provided by generated shear force.
• Steel quantity must be at least 4% of the concrete section to avoid fragile breaks in the pillar.
• In seismic zones, the amount of steel will adhere to minimum and maximum quantities to deal with thermal and rheological load as well as fire.
• Steel amount is figured in percentage of the relationship between the area of ​​the steel section and the concrete section.

Arrangement of Reinforcement in Supports

• The main reinforcement is made up of at least four bars in square or rectangular sections and one in each corner in polygon sections.
• All corner bars must be tied, with one out of every two remaining bar tied.
• Separation between bars must be no more than 30 cm.
• The thinnest bar must be no less than 12 mm in diameter.
• To make pouring easier, the least separation distance should be equal or more than the greatest of these values:
  • 2 cm
  • Max diameter of the largest reinforcement bar.
  • 1.25 times the nominal size of the aggregate.
• If there are a high number of longitudinal bars, place them in groups of no more than 4 bars to ensure minimum separation.
• Use an equivalent diameter size equal to the sum of bar areas to take into account the magnitude of coatings and minimum distance to adjecent armatures is needed.
• Bar diameter must be less than 50 mm.
• In verticaly compressed pieces bars can be up to 70mm.
• Use transversal reinforcement, armatures, hoops and stirrups when longitudinal reinforcements are subject to compression.
• These help limit buckling, reinforce concrete’s core, and help withstand winds, impacts, and seismic load.
• Section sizes for transversal reinforcement should be at least 0.25 x max diameter of longitudinal one.
• Diameters are commonly 6mm to 8mm (10 mm are more difficult to bend and compact).
• Hoops have closed configuration but stirrups do not, with the term "hoop" commonly used to mean transversal reinforcement.
• The hoop stops buckling so separated loose bars should be avoided.
• To prevent buckling, all bars separated by more than 15 cm must be secured.
• If separation between (vertical) longitudinal bars is more or equals to 15cm, place a second hoop group or a fork of equal diameter/separation as stirrups.
• Max separation of hoops to longitudinal reinforcement should not exceed the lesser values of:
  • 30 cm, the column’s smallest side
  • 15 x Ømin, with Ømin being smalles diameter to the longitudinal armature.
• Around curves, overlaps, or concentrations of tension, place a second hoop 5cm from the weld for better compaction.
• To deal with high horizontal stresses from seismic activity, fasten the hoops at the core and base of each column, 5-10 cm apart.

Types of Girders in Concrete Structures

• Girders in reticular structures mainly endure gravity loads, leading to primarily simple bending loads.
• They may deal with axial stress, combined flexion from horizontal wind actions.

Girder Sections

• Concrete girders may have T or I sections capable of resisting flexion however are reserved for prefabricated forms.
• In site-cast girders employ rectangular sections in three layouts:
  • Cantilever girders featuring deeper section than the slab/framework with a section that stands out
  • Flat girders are wide and shallow, flush with the framework
  • Jump girders resolve changes in elevation between sections through the superioir or inferior face
• It is easier to compact girders due to positioning during the pour. Their width must be at least 20cm.
• Girders have longitudinal and transverse reinforcement differing in function.

Arrangement of Girder Reinforcement

• Longitudinal armatures are:
  • Main reinforcement that endures flexion tension, so are arranged on the lower face in the span’s center or upper face at embedded ends. Also has a la length within the stress area.
  • Assembly armatures that complement girder reinforcing when not all four corners feature longitudinal reinforcement
  • Skin Armature which are placed to connect contiguous bars apart by 30cm to avoid fissuring and buckling if the girder>60cm
• Minimum geometry should be a 3.3% on the tensioned side for B400S steels, and 2.8% for B500S.
• Place a minimum armoring of 305% on top of the designed armature.
• Check the geometrical steel amount, because there is also a minimum mechanical amount constraint that avoids breaks for lack of labor

Transversal Armoring

• Traverse armatures or stirrups handle shear-generated tensions and prevent buckling in longitudinal reinforcement.
• Transversal reinforcement avoids cracks from shear stress: in this case, optimal placement to the fault would be orthogonal in placement with an inclination of 45gradees.
• For simplicity, it is placed vetically
• To follow in sizing dimensions, each transversal armoring will have the following:
  • Use a diameter >0.25Ø, and never less than 6mm.
  • Max section of stirrup sections should be 60cm or 0.75d (with the height of the girder).
• Strirrups will be the mos unfavorable of:
  • 30cm, or the measurment of the shortes side of the girder, in centimeters.
  • 15 Ømin with that being the compression bar of least, diameter.
  • The height multiplied by 0.75 of the viga.
• Sections are related to the shear supported (also, separation of the stirrups).
• It is common to arrange stirrups uniformly to avoid the need to adjust stirrups with reinforcement needs.
• In the case of punctual loads, shear effort augmented and and needing to increase stirups as well.

Reinforcement Coating

• Coating is based on endurance factors, with a basic value that raises with control.
• If the jobsite building has a close-in control, make pre-made, or building on-site under normal control, use values in 0,5,10 grade.
• Basic coating function is environmental showing, resistance to compression, and longevity.
• Coating standards commonly measure 25mm to 3mm.
• Coating comes in geometric type or mechanic which serves in outer element to the reinforcement’s gravity.

Resolution of Nodes and Encounters

• Columns rise from a foundation, over walls, or exceptionally over girders.

Pillar-to-pillar tie

• Deals with continuity of piles from floor to floor, with armatures assembled in shop.
• At the bottom, the armature joins the longitudinal pile armatures, creating a lap joint.
• At the top, the armature will equal beam face plus overlap/union with upper pile, using additional steel and binders.
• Section changes are resolved in girder faces as long as the grade does not exceed the 1/12 grade.
• For a beam resting along a facade the grade becomes symetrical.
• Horizontal anchors in fin, doubling steel over the section, provide continuity when longitudinal steel cannot be extended.

Girder-to-pillar nodes

• These spots have high armature amounts.
• Set the reinforcement support 5 cm from the labor stop.
• Supports can be extended on pillars along a forjado or built on top of pilars.
• Stirrups inside the joints, at 5 cm, and at the same height.

Run Control of Armored Concrete Structures

• Recepting the components must follow the material’s assignment in construction.
• Every component has a CE marker for control or documentation registries.

Element Execution Runs

• Create foundation and pilaster maps with labeled axes.
• Viga work is done the same for all types: viga armoring > framework pouring > concretion.
  • Flat viga pouring is done, it´s important is that the framework have negative bars, is the order it had to be done for good placement. – If viga has embeded supports, framework will be done before or after forjado.

Execute phases

Framework

• Frameworks are made of wood, plastic or metal. Avoid metal on cold or full sun, hot weather.
• Formed by:
  • Giving form to support and taking care joint are airtight. Level, plumb and concrete.
  • Viga must maintain horizontal surfaces and vertical faces in all angles.

Set up Armoring

• It´s placed steel, grease or any sort of harming ingredient.
• Reduce different types of steel or resistance that can be confused one for another.
• In pillars: leveling, and fixing the armature support or doubling and tying bars/supports. The binders are tied and set apart 100 -200cm so separators can be mounted to steel or in 3 level spans.
• In all Vigas: Place on-site and armored forjado, place longitudinal armoring and binders at desired separation, along with accessories or ties.

Concreting

• Poured concrete won´t come with segregation or mass, and sections are not diminished as well.
• During pouring, avoid components like framework pieces falling, and proceed with gentle compacting during pouring in sections to compact along section.
• It´s impossible to pouring concrete in runs so plan joint for better work.
  • Constructing is done.
  • Pour base from floor, or in each span or run.
  • To avoid any sort of damage, concrete can be fisured.

Retraction Joints

• The distant to make sure the retraction joint is equal the hirogremic conditions at concrete time, steel amount and type.
• Distances vary, and the joints serve for contraction.

Types of Joint

• In the support, it´s not needed and will do concrete by parts or level spans; if the viga is long then retract with forjado type so concrete is done in good way.
• In the middle to cut the effort.
  • It happens at around a 45-grade in the joint, by cleaning and vacuming as well. The joint will need humidity.

Steel Frameworks

• The following are main topics when it comes to steel works. The follow parameters will follow in with time, usage resistence, and weather too.

Appendices

• Main themes are in CE document and is sintetized in follow acts.

Appendix 1: Frameworks:

• Consist of: a mix temporal structure and with pre-assigned load. It will work to give resistence, and that own light wheight is insignificant. It´s deformability in estructural members and shapes with cuotas that must maintain.
• Estanqueidad:
• Easy to Assembly:
• Reusable and maximized.
• Textury.
• Protecting and curing the concrete.

Classifying

• With varied topology of framedwork with classifying different types:
  • Type of:
    • Seen or hidden
    • Recurrent
• By shape:
  • Plain
  • Curves
• Shape:
  • Mixture
  • Wood
  • Metálica sheet
  • Plastic and ceramics-cement.

Elements employed

• Timber
  • In good comportment.
    • Tight.
    • Isolate Capability.
    • Easy to Shape modify.
    • With a 1-300 kg capacity force as well as 30-60kg.
• Metals
• Difficult to SHAPE when it comes to set up, implication is important.
• Skin elements: 1-1.5mm sheet to support.
• Set of cimbria.
  • Extensibles metal to handle stress
  • Metálicos puntales with a resistence of 5-1500/200-250 kg.
  • Quatro puntales to support loads.

Specials Setups

• Advantages are the high-paced execution, quiality and maxed-resource retrieval.
• disavantage it`s: complijity, and cost, as well as an installation for easy access.
• Needs personal special to run and it´s rigidity in design.
• They are running in industrial or edifice.

Appendix 2: Hormigonado Placement

• Main objective is fabrication and to place and run concrete on the field.
• A quality hormigón has to be central mixed, and stirred. Time dictates a homogeneous mixer.

Trasport

• In the centre mixing place the trasporter must set constant rpm. To make mix correct in site, rotate in good speed when done.
• Tranfer Time needs to be limited to set mix before expire.
• With big transports apply extra to retard mix.
• Avoid expose mix or let it fall on the ground to keep most of its benefits.
• Placement of mix is done in vertido or with compaction.
• VERTIDO set the mix and separate compounds and follow.
  1. Do it.

No to Set to Fall

• Don’t make a height greater than2mt. As it loses compound, to deal with this, use a hose.
• Avoid mix hitting walls or use a canal.
• Set in tongadas less 60cm, compacting in between.

Bumping With the Mix

Compacting

• Run in vibrating mix to order, expelling air on the mix. Gentle stir to avoid segregation, making it well.

Steps

• Picando to hit the mix with a light support touch.
• Vibrating to set vibrations with motor. Vibrating through the mix with needles. Set surfaces with rules.