Structural Analysis: Specification of Loads for Plates Elements in STAAD.Pro

Dear reader as we promised in the last post, we are now discussing about specifications for assigning load on plate element in STAAD.Pro. At first we will know what types of loads are usually applied in structural model of STAAD.Pro. on such elements.

These are:

a. Concentrated load in particular location within the plate element

b. Uniformly disturbed pressure on plate element

c. Partial pressure uniformly distributed on particular portion.

d. Pressure that varies linearly over element

e. Load induced by temperature change

f. Temperature load induced due to temperature variation between bottom and top surfaces of desired plate element etc.

Now we will provide information about how load can be assigned either global or local directions in most common loading conditions:

-joint loads on elements are assigned globally

 -concentrated loads provided in any specified location, defined by the user, depending on actual structural loading conditions, may be assigned both globally or locally.

-uniform pressure to be assigned on plate element may be assigned either by globally or locally

-partially distributed uniform pressure to be assigned on a particular portion of element to represent actual loading condition may be assigned by globally or locally

-pressure varying linearly on plate can be specified locally

In case of global direction of assignment the assignment axes are fixed for element but in local assignment methods the axis are shown in particular loading window. The sign convention (either +ve or -ve) are also given in loading window. In case of facilities of both global and local assignment, the both axis systems are explained in loading window.

How are Admixtures Measured in Ready Mixed Concrete?

We have published post regarding measurement specifications for water in ready mixed concrete industry. Here in this post we will discuss about the measurements requirements of admixtures for concrete before entering them in to batching plant or truck mixer. There may arise a question-why measurement is so important. This is the specifications where tolerance of quantifying each constituents of concrete is provided.

Admixtures are important constituents of concrete that are used to render special properties to concrete or to change dosage of any constituents of concrete in mix to form a strong or impermeable or more durable concrete. Admixtures that are found in powdered form should be measured in mass. Those which are liquid can be used in batching by measuring either in volume or mass.

Admixtures that are not derived from mineral resources(mineral admixtures), as discussed above can be measured in either volume or mass, should have accuracy level of -

±3% of total admixture requirements or ±Dosages or amount of them required for 50 kg (100 lb) of cement

Between two conditions greater values are taken into consideration.

Now do we know what the mineral admixtures are? They are:

a. Coal flyash

b. Silica fume

c. Blast furnace slag granulated in ground

d. Or other pozzolanic admixtures

But we have missed an important information about mineral admixtures. This is-mineral admixtures are excluded in this specifications for admixture measurements. This is due to accounting mineral admixtures in measuring cement in ready mixed concrete. In the next post we will learn about cement and aggregate measuring specifications.

An Important information we can include, mechanically operated admixture dispensers are used in modern batching for ready mixed concrete industry. This dispenser can adjust variations of degree accuracy. But a simple calibration of this is recommended before use. This post is from ASTM C94-dear reader you have noticed that we providing information regarding concrete and foundation engineering from different Codes and Standards in simplified form. Here you need to switch one article to another article to gather an overall idea about any specification. We are providing all necessary definitions and specification to understand any topics except in some long explanation-there e also providing necessary link to just click to get information. Please encourage us by reading and commenting. We are doing everything to make popular this blog and to provide one stop service for our reader.

What are the Usual Shapes of TAPERTUBE Pile in Foundation Applications?

In the previous post we have discussed about TAPERTUBE pile application in foundation construction of different terminals of JFK International Airport. Now in this post we will discuss about shape and size of TAPERTUBE pile.

The test conducted at JFK Airport on TAPERTUBE pile were used a 25’ long pile section with bottom section of 8” diameter and top section of 18” diameter. The piles were made of 0.312” thickness steel having 12 sided polygon shape. The steel was of 50 Ksi grade. We are discussing this test as this test brings success to TAPERTUBE pile and adopted in the next terminal buildings of JFK and then spreaded from this airport to different highway, airport and railway structure construction. After driving a concrete of 5000 psi were poured. This was for testing 150 ton capacity of pile.

It is worth mentioning that the polygon shape having 12 sides is rounded at top portion of taper mechanically. This rounding technology is still using in this patented pile technology.

TAPERTUBE piles can be of various shapes and also of various sizes to meet geotechnical and structural considerations. As discussed above polygon shape having 12 sides is most common application. The usual sizes vary from 8” to 24” for bottom to top diameter and this is tapered through a length of (10-35) feet. As tested before 50 ksi (grade 50) steel is used to manufacture this pile. The thickness assigned ranging from (3/16” to 5/8”).

As mentioned earlier, the circularization of top portion of polygon provides conformation of diameter of extension as steel pipe. To facilitate it butt welds used to ensure full strength development of piling elements.

These types of piles have been found effective in granular type soils. But these types of piles used in cohesive soil and found performing well. But a few tests were done in cohesive soil. We are waiting for elaborate test results in these types of soil.

Structural Analysis: Modeling Rules for Plate/Shell in STAAD.Pro

Dear reader we have published a series of posts regarding import drawing from AutoCAD to STAAD.Pro. Next we have provided information about structural system, P-∆ analysis of structure and also about plate/shell that can be handled with STAAD.Pro. Now we will penetrate deep through the plate and shell. Dear reader we will also with ETABS with you. Perhaps we have provided plates in our different projects but do we know how to use it, what is the efficiency of plates. Dear reader we will discuss this fact here.

We should remember the following modeling rules related to geometry while providing plate/shell like element in our structure:

a. Perhaps we have found many warning before completion of analysis. Most of them are related to material properties, bad shape or warping of element x,y,z…..etc. Some warning instructs to orient element clockwise or counter clockwise. Regarding plates/shells it can be concluded that in assigning nodes, in input data, to particular element; it should be specified in either clockwise or counter clockwise orientation. To have better efficiency, a sequential numbering for similar element is required.

b. In this program a fifth node is generated automatically at the center of element. It is fictitious one.

c. There have a limitation in aspect ratio of element. These should not be beyond the limit. The limitations are as follows:

Preferred –(1:1)

Not less that (4:1)

d. No distortion of individual elements is allowed. There have limitation in the angular difference between two adjacent elements of this type:

The limitation is preferred <90⁰

Must not >180⁰

Dear reader we will finish this post here. But in the next post we will meet with the solution of question how are loads specified in plate elements.

Development of Tapered Pile in Foundation Application

In this post we will learn about a pile that is not classified with material but with the shape. We have so far discussed about piles that have uniform section whole through the length except under-reamed piles. We have published many posts about under–reamed pile in this blog. You can read this if you want to have information about it.

The driving and bearing advantage of the tapered pile was not new in foundation construction industry. Many years ago, this technology was adopted considering its ease in driving. In some soil, where straight sided piles are not providing substantial capacity, the tapered pile facilitates good performance providing expected capacity assumed in design.

The tapered pile provides end bearing with frictional resistance combinedly by the wedge action of taper pile that are greater than combined action of end bearing and side friction of a cylindrical pile. The timber pile was the first known tapered pile that’s application had been found from many years in ancient structures. Perhaps the shape of the tree inspired to use such pile in foundation in tapered form with providing small section in down and large section in top which receives impacts from pile drivers.

The true tapered pile was found in market from Raymond standard Taper Pile. After that Union Metal Monotube Tapered piles were arrived this is still available in the field. Now-a-days all tapered piles are in tubular shape made of steel and filled with concrete after they have installed.

The most successful application of tapered pile is TAPERTUBE PILE. The British Airways Terminal of John F. Kennedy International Airport (JFK) and in international Arrival Building (IAB) of the same had successfully used this technology. In the next post we will discuss about details of application of TAPERTUBE PILE in those projects.

Development of Fiber Reinforced of Polymer Composite (FRPC) Piles in Foundation Applications

As discussed in early posts, regarding pile classification, we know that piles may be steel, precast concrete, wood, cast-in-situ concrete and of another types. We will discuss here a relatively new materials fiber reinforced polymer composite (FRPC) piles to rehabilitate pile foundation and new one. Of these cast-in-situ pile is bored piles but rest types are fall in the categories of driven pile.

We are concerned here with driven piles as we will discuss about FRPC piles. Being relatively new materials in driven piles, it is required to investigate extensively about the properties and response of these piles under driven impacts and as well earthquake impact.

In 1998 a riverside project was needed to be rehabilitated. This is Hudson River Park in Manhattan. More precisely on this time the rehabilitation began. In this project, it was needed to be replaced enormous amount of piles (100,000) that supports lightweight structures. Considering this large scale rehabilitation and other rehabilitation projects to come in the next, the researchers were looking for an alternative pile material. The rehabilitation becomes mandatory as steel corrosion, concrete deterioration and timber piles were found vulnerable in marine environment. This situation forced engineers to select an alternative material that have high resistance to degradation. Then FRPC piles were selected due to its strength and degradation resistance.

At the same time Federal Highway Administration known as FHWA initiated some research project on the long-term performance of these pile. They have conducted research for finding feasibility of FRPC piles for mainly highway and facilities related to highway to replace conventional materials vulnerable to deterioration in hostile waterfront or marine environments. They established that FRPC may be a competitive alternatives against deterioration suspected pile materials in aggressive exposure environments. Due to environmental reason chemical treatment with toxic agent was also kept limited and State Department of Transportation are conducting major rehabilitation problems to restore vulnerable structures, led to choose FRPC bearing piles to use in infrastructure.

What is the Long Column Behavior of Pile Foundation?

Dear reader we have published about classification of piles based on load transmission mechanism and real situation in this load transmission. Here we will discuss about the error in assumption regarding point bearing pile penetrating through soft loose deposit.

We know that some piles derive support from point bearing stratum. There have a wrong consideration that piles are in free standing column condition when they are surrounded by soft soil even in fairly stiff soil. We know that such a long member have every risk of buckling when they are loaded axially.

But from theory and experience as well clearly produce that there have no possibility of buckling even that are surrounded by very soft soil which were erroneously considered to be buckled under axial loads. When some lateral components of load come in addition to axial loads, the consideration have to be modified. But in this post we will not discuss about lateral component. In the upcoming posts we will discuss about design consideration for piles subjected to both axial and lateral forces and design procedures for piles subjected to both axial and lateral forces.

Now, designer limits working stress in materials of piles under direct compression by providing sufficient section and reinforcement in case of concrete pile and choosing a suitable method of drilling or driving. We know some piles are made to tapper to their tip with the gaining of depth. In such piles, obviously, the tip section is critical section to be checked. In the previous post we have discussed about working stress limitation and recommended slump for concrete pile construction. Once designer ensured that the tips are not failed in overstressing, the capacities of piles that derive main support form end bearing depend on surrounding soil materials. In the next post we will discuss how an end bearing pile can be used to have some skin resistance too.

Achieving Quiet Concrete Pavement with Continuously Reinforced Concrete Pavement (CRCP)

Dear reader you can remember that we have published British guidelines to provide whisper concrete. In that post we came to know the term continuously reinforced concrete pavement (CRCP). So far we learned to provide a quiet concrete pavement by using either exposed aggregate concrete surfacing (whisper concrete) or re-grooving method called concrete grinding and grooving technology. Regarding whisper concrete and grinding and grooving we have published several posts. So far we have learned to treat a worn out concrete pavement with either resurfacing or re-grooving. In this post we will learn about the main structural concrete pavement upon which the treatments are provided.

Our aim is to provide a concrete pavement that naturally reduces noise pollution and with application of treatment it is ensured an excellent quiet riding surface for vehicles. In this construction method engineers provides longitudinal joints rather providing transverse joints. This is achieved by constructing a concrete pavement with continuous reinforcement in longitudinal directions.

By eliminating transverse joints, this pavement offers a excellent smooth riding surface. This joint less concrete pavement practically does not need maintenance. As we know that a joint is a weak plane, which can be penetrated by moisture, chemicals or differential settlement of concrete pavement can be occurred. We have published many posts regarding slab foundation raising, repairing and rehabilitation. You can read this for additional information.

The elimination of transverse joint is not mandatory in bridges or the structural paving systems. In the United Kingdom this method of paving concrete used as structural base for road. Now-a-days its use is increased extensively because of tough and free from maintenance behavior. Regarding skid resistance it is treated with whisper concrete or grinding and grooving techniques can be used to maintain it. This treatment of re-grooving method also reduces noise pollution.

Modern highway engineering have taken concrete pavement as a substitute of traditional flexible pavement and overlaying with asphalt as technological advancement and raise of asphalt prices makes both options have same initial cost. As concrete option have more longevity and less maintenance requirements, concrete is dominating as pavement constituent materials rather asphalt or bitumen.

How are Pile Classified Based on Load Transfer in Foundation Engineering?

We have published post regarding classification of piles depending on materials and method of installation. Now we are adventing a classification which is most important in pile foundation design. Depending on load transfer mechanism pile are classified in two types:

a. Point-bearing piles 

b. Friction piles

We will have general idea about point-bearing piles and friction piles in this post. In the next post we will discuss each classification elaborately.

At first we are discussing point-bearing piles. This classification is based on the sources of support that brings capacity to piles. This type of pile derives support from rock or relatively strong soil in which the tip of pile is rested. There have no or little support from the surrounding soils.

In case of friction piles, the pile derives its support mainly from surrounding soils. This type of pile provides its resistance from the shearing resistance, developed between the pile and soil i.e. lower part of the piles do not play important role or developed a very small resistance.

The way we have discussed about load transmission is very simple. But actual situation is not the same, as we classified pile in two categories. In general condition the relative density and stiffness of subsoil shows an increasing trend with the depth of penetration. So in this situation piles are penetrating through upper soft layer and gradually they are confined in stiffer layers to reach required bearing capacity. This pile derive considerable amount of support from surrounding soil materials in lower portion of stiffer layers, still it derives large/ main amount of support from end bearing stratum. Thus the situation demands an actual performance of both supporting categories.

In piling work and pile designing, it is matter of great importance to take right discussions for a most appropriate pile’s type to make it suitable for particular geotechnical and site conditions. Behavior of pile during driving control many discussions. So it is not possible to provide a simple or definite formula for the best guidance for an inexperience engineers. So, sound knowledge of transmitting load to surrounding and soil beneath are the invaluable asset to produce a good engineering judgment.

How is Water Measured in Ready Mixed Concrete Batching?

. In last post was regarding inspector authority in concrete construction control. We have learned that with the best materials we cannot produce a best even fairly good concrete without right practice. Here We will discuss here about measuring specifications for mixing water to be added to concrete. We are discussing this topic according to ASTM C94/C.

First we will learn, in how much form, water can present or added to particular batch. Here we are listing how mixing water may consist. They are:

2FR Concrete Water Management System specially designed to record flow water to concrete batch that also provide alarm when washing out after pouring concrete is occurred.  

1. Water added in the batch mixing

2. Added water in ice form to the batch

3. Water appears from the moisture, present in aggregate in its surface.

4. Equivalent water from the admixtures

In the mix design we will use the total mass or volume of water from all sources. Surface moisture or admixture equivalent water is derived from standard test and procedure.

Now question is the accuracy in water measurement. The water measured either by mass or volume should have an accuracy of 1% of water that is totally required in mix. The ice added to the mix, in the special situations, should be measured by weight.

Now what about truck mixer? In truck mixing in sometimes there has some amount of wash water in the drum. The retained water that is not discharged to be used for next batching should be measured accurately. In case of where retained water cannot be measured accurately or it is impractical to measure this water, it is wise to discharge all water before loading materials for next batch. The total water, including above discussed wash water, should be measured and weighed in an accuracy of 3% of water that are designed for a particular batch.

Adoption of Concrete Grinding and Grooving Method in United Kingdom in Restoration of Concrete Pavement

In the previous post we have learned about application of exposed aggregate concrete surfacing in different junctions of United Kingdom. In this post we will learn about regrooving method of restoration of concrete pavement. In this method we will not provide any overlay rather we will introduce a method of grinding and grooving of exiting concrete surface to reduce noise pollution and provide required skid resistance to avoid vehicular loss of control during rainy season or other unexpected situation that can lead to accidental hazard.

This noise reduction measures are used in many provinces United Kingdom-as example we can include-

a. In essex, A13 Chelmsford bypass

b. In Suffolk A12 etc

They are serving for many years successfully. This method also adopted in United States for many years.

This method uses a plant that has diamond tipped blades to saw the existing concrete pavement. The blades are spaced closely to cut traction and drainage grooves on the existing concrete pavement. The results of application of this machine are closely spaced texturing grooves. This grinding with diamond tipped saw leave a high level surface texture that provides skid resistance to the restored pavement.

Now question is-can these grinding results structural failure of concrete pavements?. It is good news for engineers that this grinding application can be used three times in separate period’s interval without hampering structural performance.

This method is proved economical as it can be provided only at the half cost of asphalt overlaying on concrete pavement. Regarding longevity, the life span of this grinded concrete surface may be 17 years without interrupting normal traffic flow for repairing or resurfacing effort. We know asphalt overlay can hardly be used after (8-12) years.

Inspector Authority on Concrete Construction Control

We have already known about the job description of inspector in construction process besides the jobs and control of structural engineers on concrete work. Here we will provide some information regarding the authority of inspector. Here contractor is provided with the information about the authority of inspector with structural engineers. The authorities are:

a. He/they can prohibit construction of concrete work before completing the preparation like 

1. Providing and stiffening forms

2. Placing reinforcement and securing the same

3. Inserting pipes for both sanitary and electrical purposes that have to be embedded in concrete members etc.

b. He/they can restrict application of methods or equipments that are not approved by respective structural engineers or not comply with specifications resulting improper construction or result inferior workmanship.

c. He/they can postpone or stop any construction process that do not comply with specifications or designed plans. Postponing is concerned with waiting for acceptance of structural engineers. Postponing or stopping is specially required where repair or removal of faulty construction is required or where the inspectors have not visited subsequently.

Stooping or postponing work or removal work of a previously completed improper construction work, reconstruction as well, should be addressed carefully considering time and cost involvement and disturbance of not matured member while removal or dismantling one or more. But sometimes considering safety of structure or quality of work, there have no way to avoid these discussions.

It is important to provide construction work with good contractor and experience job inspector as well who have through idea about high-performance concrete. Especially construction in pronounced seismic regions, they should maintain quality of work in concrete construction work as their have many issues in site performance, even plan-mix concrete or precast concrete elements, that make a best construction materials to be cast in bad condition. The standard and manuals from American Concrete Institute, standards from American society of testing materials and also selected publications from National Ready-mixed Concrete Association, Reinforcing Steel Institute, Portland Cement Association and Institute of wire reinforcement, should be followed for reference of both contractor and inspectors.

Becoming Popular of Cutting Edge Technology-Polyjacking in New England for Slab Foundation Repair

In the last post we have discussed about repair technique of curled slab foundation. The secret of this rapid repair is polyurethane foam injection. Here in this post we will discuss a cutting edge slabjacking method. This is not new term to you, as we have discussed a little bit in last post about polyjacking. This method is successfully used in many sites of New England and becoming popular in western United States.

We have few ideas about polyjacking. Now we will discuss the scope of this special type of slabjacking method. This method is successfully used in wide range of work like raising sunken concrete slab-on-grade foundation, pools patios, warehouse floors, concrete highway and walkway made with concrete. 

Engineered Foundation Technologies a foundation expert team provides many successful polyjacking over New England. Now we will learn how they do this. Two part of liquid resin of polyurethane is injected through concrete in the process. These resins penetrate beneath the concrete and fill cavities, expanding to form rigid foam that serve as structural element.

The most important thing of this slabjacking is the repaired or raised slab gets ready within 15 minutes. Even under heavy traffic it performs good in the most earliest period of repair. The polyurethane foam has quick setting properties that make it supreme repair material.

Moreover a factor cleanliness is important in selection of slabjacking process. In this fact also polyjacking has outnumbered the foundation slabkjacking. Polyjacking is clear choice to repair engineer as almost pack up is done with completion of work. In the business and industrial floor it is very important to leave work space for service within short period, polyjacking serves the service best-almost there have no competitor of this method in concrete repair industry.