Edge Column Research Articles

Effect of spandrel beams on strength and behaviour of column-slab connections

Spandrel beams are commonly used to strengthen the connections between slabs and edge columns in flat slab structures. The present study uses experimental and analytical means to improve understanding of the behaviour of these connections, especially when spandrel beams are used. The parameters considered are the spandrel beam size and reinforcement ratio, the width of the inside column slab interface, and the type of straining actions to be transferred through the connection. The efficiency of using a slab extension (beyond column outer face) instead of a spandrel beam is also studied. Based on the failure mechanism observed during the tests, a new analytical method to predict the strength of edge column-slab connections is suggested. A second analytical method is also developed while being based on a simplified failure surface. The accuracy and reliability of both methods are thoroughly assessed in this study.

Design for punching shear in concrete: critical review of Canadian Standard CSA-A23.3-94: Discussion

The authors review the provisions in CSA-A23.3-94 for punching shear in concrete slabncolumn connections. They identify two items that are missing from this standard: (i )a value of αs = 2 for corner columns when determining the fac- tored shear stress resistance for the concrete and (ii) an upper limit for the stirrup spacing of s ≤ 0.5d when stirrups are used for shear reinforcement. The writers agree that these two omit- ted items should have been included. The authors also indicate they believe that the provisions for slab shear reinforcement when such reinforcement is re- quired have been changed from the previous edition of the Standard in a manner that can lead to unsafe design and refer to three tests that they claim substantiate this belief. These two items are discussed separately. The authors assert that CAN3-A23.3-M84 limits the shear stress due to the combined effect of Vf and (γvMf)x and y to 0.2λφc√ fcon a critical section outside the shear-reinforced zone. In the opinion of the writers, this is highly debatable. Clearly, this is the interpretation provided in Chapter 10 of Concrete Design Handbook (CPCA 1985) where, for an edge column, the shear moment interaction is calculated on a sec- tion outside the shear reinforcement. It is of interest to note that a similar example (18.4) can be found in Notes on ACI 318-89 (PCA 1990). This is relevant, since both CAN3- A23.3-M84 and ACI 318-89 use almost identical language regarding combined shear and moment transfer at slabncol- umn connections. In the PCA document, however, only the average shear stress due to Vf is considered at the critical section outside the shear-reinforced zone. In the opinion of the writers, neither CAN3-A23.3-M84 nor CAN3-A23.3-M94 re- quires the combined effects of shear and moment to be con- sidered at any section other than that located d/2 from a support, concentrated load, or change in slab thickness. Ideally, this discussion should depend not on semantics but on a consensus understanding of the behaviour of slabncolumn connections. The writers do not believe that there is as yet such a consensus. At best, the procedure in the Standard provides a reasonable metric of the severity of loading on a connection. It has been calibrated for a critical section d/2 from the column face. To extrapolate the procedure to sections located at greater distances from the column places inordinate faith in the fun- damental soundness of the procedure and ignores profound changes in the behaviour of the slab as distance from the col- umn support increases. In analyzing the test results, the authors do not appear to have considered all of the provisions that may govern the strength of a connection. Clause 13 of A23.3-94 gives three possible limits on the strength of a shear-reinforced interior slabncolumn connection. The first of these is a straight-line shearnmoment interaction calculated for the critical section located d/2 from the column face. The end points of the inter- action are given by the shear capacity of the connection with no unbalanced moment and the maximum unbalanced moment capacity with no net vertical shear. The second limit is on the magnitude of the average vertical shear outside the shear-re- inforced zone, called Vcode by the authors. Finally, Clause 13.11.2 requires that flexural reinforcement sufficient to resist γfM be placed within a band c + 3h. This provision places a flexural upper limit, Mflex, on the magnitude of the unbalanced

Punching Shear of Continuous Flat Reinforced Concrete Slabs

This paper presents experimental results for the punching shear of a two-bay-by-two-bay flat reinforced concrete slab. The results show that the interior column slab connection is more critical in punching shear than the edge and corner column connections in a properly designed multibay flat slab. Large flexural cracks indicative of steel yield were evident at all connections where punching shear failures occurred. Supplementary supports can increase punching shear capacity by about 30 percent at edge column connections. An empirical method using a shear perimeter around the loaded area is developed. The code provisions of ACI 318-89, BS 8110-85, and the CEB-FIP 1990 Model Code were recalculated in terms of mean concrete strength using published experimental results to remove their conservatism. Comparison shows that isolated punching tests can represent the punching shear behavior of interior column slab connections in continuous slab systems. All four methods were adequate to predict the capacity of edge and corner column connections under gravity loads. Finally, the code format equations and the proposed equation were recalculated to obtain 95 percent characteristic values.

水平力を受ける杭支持建物の破壊性状に関する実験的研究 : その1 変動軸力を考慮しない解析結果との比較

Three types of building models were tested by repeated and reversal horizontal loading to investigate the collapse mechanism of the models. Type 1: fixed on rigid base. Type 2: supported by piles in a very weak soil model which consisted of Kaolin clay with cement. Type 3: supported by piles in a weak soil model which consisted of Kaolin clay with cement. For Type 1, all beam and column edges yielded up to the plastic strength of 3.5 tf as the testing result. For Type 2, the pile heads and edges of footing beams yielded at the plastic strength of 1.7 tf. For Type3, pile heads, edges of footing beams and edges of members yielded at the plastic strength of 3.1 tf. Nonlinear frame analysis for the models with and without soil springs were carried out to compare with the test results. Experimental results were simulated very well by this analysis for Type 1. For Type 2 and 3, results of analysis showed good agreement with experimental results for the load-deflection relationship but there is a little difference for the collapse mechanism of super structure.

Efficient Self-Simulation Algorithms for Reconfigurable Arrays

There are several reconfiguring-network models of parallel computation that are considered in the published literature, depending on their switching capabilities. Can these reconfigurable models be the basis for the design of massively parallel computers? Perhaps the most fundamental related issue is virtual parallelism, or the self-simulation problem: Given an algorithm which is designed for a large reconfigurable mesh, can it be executed efficiently on a smaller reconfigurable mesh? In this work, we give several positive answers to the self-simulation problem. We show that the simulation of a reconfiguring mesh by a smaller one can be carried optimally and using standard methods on the model in which buses are established along rows or along columns. A novel technique is shown to achieve asymptotically optimal self simulation on models which allow buses to switch column and row edges, provided that a bus is a "linear" path of connected edges. Finally, for models in which a bus is any subgraph of the underlying mesh, efficient simulations are presented, paying by an extra factor which is polylogarithmic in the size of the simulated mesh. Although the self-simulation algorithms are complex and require extensive bookkeeping operations, the required space is asymptotically optimal.

The influence of a biased limiter on a collisionless magnetised alkali plasma column

We report preliminary results of an investigation of the global properties and the stability of a magnetised collisionless plasma column under the influence of a biased limiter. For higher negative biases the diameter of the plasma column can be decreased until the plasma is completely quenched. For smaller positive biases only the radial density gradient and the radial electric field are affected and the oscillations at the plasma column's edge change their frequency and band width. Also the electron current-driven potential relaxation instability can either be enhanced or totally quenched by the limiter bias.

Studies on Concrete Slabs with Stud Reinforcement in the Vicinity of Edge and Corner Columns

Studies on Concrete Slabs with Stud Reinforcement in the Vicinity of Edge and Corner Columns

Liquid-metal tokamak divertors

Both limiters and divertor plates of the reactor scale tokamaks are known to be subjected to extremely high heat loads. The problem of quasistantionary heat fluxes (∼107 W/m2), removal, and even the more severe problem of plates protection against impulse heat release on the order of ∼107 J/m2 during (0.1−1)×10−3 s, are the most critical issues related to divertor regimes in tokamaks. Melting, cracking and other damages of plasma facing components may occur in these regimes. Thus a demand arose to provide the possibility to replace these critical components easily. The easiest possible solution is to replace the traditional contact refractory materials with liquid metals. The simplest realization of the idea was proposed already in the UWMAK project, where a rigid divertor plate was replaced by liquid lithium flow. However, some intrinsic properties of lithium impede its practical application: 1) burning under contact with water; 2) small difference between melting and boiling temperatures. Another candidate material, liquid Ga, is believed to be more adequate (Tm=30°C, Tb=2400°C). On the T-3M tokamak the first encouraging experiments were performed where a liquid Ga jet-drop curtain was tested as a tokamak limiter. The limiter is analogous to one which uses small refractory balls falling down through the plasma column edge. Experiments with a liquid Ga sheet limiter have also started. Experimental results and possible perspectives are discussed.

Reality check: Personal quiz on personal computing

Arriving at the end of a three‐year “semester,” it's exam time at the trailing edge. Didn't the author mention that there would be a test? Sixty‐six “true or false” statements test your knowledge and understanding of the personal computer field at the beginning of 1992, and the extent to which your view of personal computing is congruent with the author's. The latter is significant because, if most of you see things entirely different, then Library Hi Tech is wasting its paper printing this column and the author is wasting his time writing it. Some of the material on this quiz comes from the last eleven Trailing Edge columns. Some does not. The quiz, and the commentary accompanying answers, are the author's way of summing up three years of personal computing before moving on to another cycle. The author also provides notes from PC literature received during October‐December 1991. It's “printer quarter,” otherwise covering a wide range of topics. As usual, all the year‐end “awards” and predictions are ignored.

Connection of Flat Plates to Edge Columns

Test results of 6 full-scale reinforced concrete flat plate connections with edge columns subjected to shear-moment transfer are reported. Two specimens had no shear reinforcement and the remaining 4 had various arrangements of stud-shear reinforcement. The results confirmed the effectivenesss of this type of shear reinfrocement in improvig shear strength and ductility. Code provisions and rules for the design of shear-stud reinforcement are compared with the test results.

Shear strength of prestressed concrete edge slab–column connections with and without shear stud reinforcement

Results are reported of tests to failure on six full-scale unbonded post-tensioned prestressed concrete slab–edge column specimens. The objective is to study experimentally the strength and behaviour of this type of connections. The variables are quantity and distribution of stud shear reinforcement and length of overhang. The relevant design equations suggested by Dilger and Ghali as well as several models by others for predicting the strength of prestressed concrete slab–edge column connections are compared with test results. It is concluded that the ACI and CSA provisions for predicting the strength of such connections are conservative, and that the presence of stud shear reinforcement is a good means of increasing the strength and ductility of this type of connections. Key words: shear strength, flat slabs, prestressed concrete, unbonded tendons, shear reinforcement, design, ductility.

Measurements of electromagnetic waves in Phaedrus-B: Bench-mark test of ANTENA wave field calculations

It is shown that the predictions of a numerical code (ANTENA) and the data of wave field measurements in the Phaedrus-B tandem mirror are consistent (±25%) for right-handed (B⃗−) wave fields and less so (±40%) for left-handed (B⃗+) wave fields in the plasma core, and that they disagree for B⃗+ fields near the column edge. Shorting out or reduction of the wave azimuthal electric fields by limiters is the probable cause of this discrepancy. The ICRF fluctuating wave B⃗ fields are shown as |B⃗| contour maps in the r-z plane, where the B⃗+ data peak at a smaller radius than predicted. The waves are characterized by different dominant axial wave numbers for the left- and right-handed circularly polarized fields.

Shear-moment transfer in flat plates

For many concrete slabs without beams, the critical design factor is the shear stress in the vicinity of the column–slab junction. This is particularly so near edge and corner columns where the shear stresses due to the unbalanced moments may account for the major portion of these stresses. The determination of these design stresses in accordance with the provisions of Standard CAN3-A23.3-M84 is both time consuming and subject to numerical mistakes. Based on these provisions, design charts were developed, which greatly reduce the amount of calculation required and are suitable for routine use in the design of slabs. The use of the charts is illustrated by examples. Key words: design, flat plate, moment transfer, reinforced concrete, shear, slabs.

Forces in the vicinity of edge columns in flat-slab floors

Synopsis Tests were carried out on four half-size models of flat-slab floors. Each model represented two panels at the edge of a building. They were tested under simulated uniformly distributed load with the object of investigating the distribution of moments and shears on the three faces of an edge column. The three force components at the pin support at the foot of the test column were measured; strain gauges were also attached to the reinforcement. From these measurements, expressions are developed which predict what proportions of the total panel moment and shear enter the column directly as bending and shear at the column face. The remainder enters via the spandrel beam or spandrel-strip. Statics then enables the torsion, shear and bending in the spandrel to be calculated,

The formation of plasma equilibrium in a Q-machine with radial potential discontinuities

A potassium-ion plasma forms in a Q-machine with mirror magnetic fields at the hotplates. Discontinuity in the thermoelectric potential at the hotplate edge produces a strong localized radial electric field that both electrostatically confines the ions and creates a high-velocity rotating annulus. Neglecting time-dependent losses, the radial equilibrium in the collisional regime with the column radius comparable to the ion gyro radius is adequately described by an isothermal single-fluid model, including both ion viscosity and rotational inertia. The radial density profiles are consistent with classical diffusion at the column edge.

Guide-line and gravity orientation of blind termites foraging in the open (Termitidae:Macrotermes, Hospitalitermes)

1. Once in several days large numbers ofHospitalitermes sharpi, like other species of this oriental genus, leave their nests for a foraging trip to replenish food stores. Foraging columns are continuous, well ordered files of marching termites, up to 300 meters long and sometimes longer, stretching without interruption all the way from the nest to the grazing area on living tree bark. Topography permitting, the foraging columns follow pre-existing guide-lines, the crest-lines on the tops of sticks, roots and other elongate objects (=crest-line trailing). On vertical substrate, like cliffs or standing tree trunks, they either proceed horizontally or vertically. During any such foraging period each individual soldier and worker leaves the nest only once. 2. Homebound traffic inHospitalitermes marching columns occupies the central lanes, outbound traffic the lateral lanes. Soldiers lead the advancing column, trail the retreating column and stand on either side of every column, facing away from the column's edge. 3. The odor trails laid down by the foraging columns are bidirectional, i.e. homebound and outbound direction are indistinguishable for the termites. Misdirected homing termites restore their correct orientation after series of head-on collisions with correctly oriented companions. 4. No outside directional stimuli, in particular the directions of light and gravity, are used byHospitalitermes to make up for the directional ambivalence of the odor trail. 5. The orientation mechanism underlying crest-line trailing, the predominant type of orientation prior to the formation of an odor trail (=primary orientation), is a geoklinotaxis: the advancing termites on a crest-line, say the top of a horizontal stick, oscillate to the sides, turning back up-slope after reaching a particular angle of downward inclination. In 50% of the cases measured withHospitalitermes umbrinus, this angle is 12–13° or less from horizontal. 6. InHospitalitermes rufus, H. sharpi, andMacrotermes carbonarius, the orientation angle between the slope direction upward or downward and the direction of walking (=angle of geomenotaxis) decreases with increasing slope inclination. InMacrotermes carbonarius body weight is one factor mediating gravity perception. 7. The orientation strategy and marching column organization of the orientalHospitalitermes-species bear some striking resemblances to those of some neotropicalEciton-species (=army ants).

The effect of pressure drifts on the plasma column edge oscillations

By applying a d.c. voltage to the aperture limiter plate a Q-machine the radial density gradient and plasma frequency were varied. The frequency shift has been attributed to a gradp*B azimuthal drift velocity. An increase of less than 2 V also changes the plasma column from a turbulent to a quiescent state.